NAME

proc − /proc, the process file system

DESCRIPTION

/proc is a file system that provides access to the state of each process and light-weight process (lwp) in the system.  The name of each entry in the /proc directory is a decimal number corresponding to a process-ID.  These entries are themselves subdirectories.  Access to process state is provided by additional files contained within each subdirectory; the hierarchy is described more completely below.  In this document, “/proc file” refers to a non-directory file within the hierarchy rooted at /proc.  The owner of each /proc file and subdirectory is determined by the user-ID of the process. 

Standard system calls are used to access /proc files: open(2), close(2), read(2), and write(2) (including readv(2), writev(2), pread(2), and pwrite(2)).  Most files describe process state and can only be opened for reading.  ctl and lwpctl (control) files permit manipulation of process state and can only be opened for writing.  as (address space) files contain the image of the running process and can be opened for both reading and writing.  An open for writing allows process control; a read-only open allows inspection but not control.  In this document, we refer to the process as open for reading or writing if any of its associated /proc files is open for reading or writing. 

In general, more than one process can open the same /proc file at the same time.  Exclusive open is an advisory mechanism provided to allow controlling processes to avoid collisions with each other.  A process can obtain exclusive control of a target process, with respect to other cooperating processes, if it successfully opens any /proc file in the target process for writing (the as or ctl files, or the lwpctl file of any lwp) while specifying O_EXCL in the open(2).  Such an open will fail if the target process is already open for writing (that is, if an as, ctl, or lwpctl file is already open for writing).  There can be any number of concurrent read-only opens; O_EXCL is ignored on opens for reading.  It is recommended that the first open for writing by a controlling process use the O_EXCL flag; multiple controlling processes usually result in chaos. 

If a process opens one of its own /proc files for writing, the open succeeds regardless of O_EXCL and regardless of whether some other process has the process open for writing.  Self-opens do not count when another process attempts an exclusive open.  (A process cannot exclude a debugger by opening itself for writing and the application of a debugger cannot prevent a process from opening itself.)  All self-opens for writing are forced to be close-on-exec (see the F_SETFD operation of fcntl(2)). 

Data may be transferred from or to any locations in the address space of the traced process by applying lseek(2) to position the as file at the virtual address of interest followed by read(2) or write(2) (or by using pread(2) or pwrite(2) for the combined operation).  The address-map file /proc/pid/map can be read to determine the accessible areas (mappings) of the address space.  I/O transfers may span contiguous mappings.  An I/O request extending into an unmapped area is truncated at the boundary.  A write request beginning at an unmapped virtual address fails with EIO; a read request beginning at an unmapped virtual address returns zero (an end-of-file indication). 

Information and control operations are provided through additional files.  <procfs.h> contains definitions of data structures and message formats used with these files.  Some of these definitions involve the use of sets of flags.  The set types sigset_t, fltset_t, and sysset_t correspond, respectively, to signal, fault, and system call enumerations defined in <sys/signal.h>, <sys/fault.h>, and <sys/syscall.h>.  Each set type is large enough to hold flags for its own enumeration.  Although they are of different sizes, they have a common structure and can be manipulated by these macros:

prfillset(&set);/∗ turn on all flags in set ∗/
premptyset(&set);/∗ turn off all flags in set ∗/
praddset(&set, flag);/∗ turn on the specified flag ∗/
prdelset(&set, flag);/∗ turn off the specified flag ∗/
r = prismember(&set, flag);/∗ != 0 iff flag is turned on ∗/

One of prfillset() or premptyset() must be used to initialize set before it is used in any other operation.  flag must be a member of the enumeration corresponding to set. 

Every process contains at least one light-weight process, or lwp. Each lwp represents a flow of execution that is independently scheduled by the operating system. All lwps in a process share its address space as well as many other attributes. Through the use of lwpctl and ctl files as described below, it is possible to affect individual lwps in a process or to affect all of them at once, depending on the operation. 

When the process has more than one lwp, a representative lwp is chosen by the system for certain process status files and control operations.  The representative lwp is a stopped lwp only if all of the process’s lwps are stopped; is stopped on an event of interest only if all of the lwps are so stopped (excluding PR_SUSPENDED lwps); is in a PR_REQUESTED stop only if there are no other events of interest to be found; or, failing everything else, is in a PR_SUSPENDED stop (implying that the process is deadlocked).  See the description of the status file for definitions of stopped states.  See the PCSTOP control operation for the definition of “event of interest”. 

The representative lwp remains fixed (it will be chosen again on the next operation) as long as all of the lwps are stopped on events of interest or are in a PR_SUSPENDED stop and the PCRUN control operation is not applied to any of them. 

When applied to the process control file, every /proc control operation that must act on an lwp uses the same algorithm to choose which lwp to act upon.  Together with synchronous stopping (see PCSET), this enables a debugger to control a multiple-lwp process using only the process-level status and control files if it so chooses.  More fine-grained control can be achieved using the lwp-specific files. 

DIRECTORY STRUCTURE

At the top level, the directory /proc contains entries each of which names an existing process in the system.  These entries are themselves directories.  Except where otherwise noted, the files described below can be opened for reading only.  In addition, if a process becomes a zombie (one that has exited but whose parent has not yet performed a wait(2) upon it), most of its associated /proc files disappear from the hierarchy; subsequent attempts to open them, or to read or write files opened before the process exited, will elicit the error ENOENT. 

Although process state and consequently the contents of /proc files can change from instant to instant, a single read(2) of a /proc file is guaranteed to return a sane representation of state; that is, the read will be atomic with respect to the state of the process.  No such guarantee applies to successive reads applied to a /proc file for a running process.  In addition, atomicity is not guaranteed for I/O applied to the as (address-space) file for a running process or for a process whose address space contains memory shared by another running process. 

A number of structure definitions are used to describe the files.  These structures may grow by the addition of elements at the end in future releases of the system and it is not legitimate for a program to assume that they will not. 

STRUCTURE OF /proc/pid

A given directory /proc/pid contains the following entries.  A process can use the invisible alias /proc/self if it wishes to open one of its own /proc files (invisible in the sense that the name “self” does not appear in a directory listing of /proc obtained from ls(1), getdents(2), or readdir(3C)). 

as

Contains the address-space image of the process; it can be opened for both reading and writing.  lseek(2) is used to position the file at the virtual address of interest and then the address space can be examined or changed through read(2) or write(2) (or by using pread(2) or pwrite(2) for the combined operation). 

ctl

A write-only file to which structured messages are written directing the system to change some aspect of the process’s state or control its behavior in some way.  The seek offset is not relevant when writing to this file.  Individual lwps also have associated lwpctl files in the lwp subdirectories.  A control message may be written either to the process’s ctl file or to a specific lwpctl file with operation-specific effects.  The effect of a control message is immediately reflected in the state of the process visible through appropriate status and information files.  The types of control messages are described in detail later.  See CONTROL MESSAGES. 

status

Contains state information about the process and the representative lwp.  The file contains a pstatus structure which contains an embedded lwpstatus structure for the representative lwp, as follows:

typedef struct pstatus {
intpr_flags;/∗ flags (see below) ∗/
intpr_nlwp;/∗ number of lwps in the process ∗/
pid_tpr_pid;/∗ process id ∗/
pid_tpr_ppid;/∗ parent process id ∗/
pid_tpr_pgid;/∗ process group id ∗/
pid_tpr_sid;/∗ session id ∗/
id_tpr_aslwpid;/∗ lwp-id of the aslwp, if any ∗/
id_tpr_agentid;/∗ lwp-id of the agent lwp, if any ∗/
sigset_tpr_sigpend;/∗ set of process pending signals ∗/
uintptr_tpr_brkbase;/∗ virtual address of the process heap ∗/
size_tpr_brksize;/∗ size of the process heap, in bytes ∗/
uintptr_tpr_stkbase;/∗ virtual address of the process stack ∗/
size_tpr_stksize;/∗ size of the process stack, in bytes ∗/
timestruc_tpr_utime;/∗ process user cpu time ∗/
timestruc_tpr_stime;/∗ process system cpu time ∗/
timestruc_tpr_cutime;/∗ sum of children’s user times ∗/
timestruc_tpr_cstime;/∗ sum of children’s system times ∗/
sigset_tpr_sigtrace;/∗ set of traced signals ∗/
fltset_tpr_flttrace;/∗ set of traced faults ∗/
sysset_tpr_sysentry;/∗ set of system calls traced on entry ∗/
sysset_tpr_sysexit;/∗ set of system calls traced on exit ∗/
lwpstatus_tpr_lwp;/∗ status of the representative lwp ∗/
} pstatus_t;

pr_flags is a bit-mask holding the following process flags.  For convenience, it also contains the lwp flags for the representative lwp, described later. 

PR_ISSYS process is a system process (see PCSTOP). 

PR_VFORKP
process is the parent of a vforked child (see PCWATCH). 

PR_FORK process has its inherit-on-fork mode set (see PCSET). 

PR_RLC process has its run-on-last-close mode set (see PCSET). 

PR_KLC process has its kill-on-last-close mode set (see PCSET). 

PR_ASYNC process has its asynchronous-stop mode set (see PCSET). 

PR_MSACCT
process has microstate accounting enabled (see PCSET). 

PR_MSFORK
process microstate accounting is inherited on fork (see PCSET). 

PR_BPTADJ process has its breakpoint adjustment mode set (see PCSET). 

PR_PTRACE
process has its ptrace-compatibility mode set (see PCSET). 

pr_nlwp is the total number of lwps in the process. 

pr_pid, pr_ppid, pr_pgid, and pr_sid are, respectively, the process ID, the ID of the process’s parent, the process’s process group ID, and the process’s session ID. 

pr_aslwpid is the lwp-ID for the "asynchronous signal lwp" (aslwp).  It is zero if there is no aslwp in the process.  The aslwp is the lwp designated to redirect asynchronous signals to other lwps in a multi-threaded process.  See signal(5) for a description of the aslwp. 

pr_agentid is the lwp-ID for the /proc agent lwp (see the PCAGENT control operation).  It is zero if there is no agent lwp in the process. 

pr_sigpend identifies asynchronous signals pending for the process. 

pr_brkbase is the virtual address of the process heap and pr_brksize is its size in bytes.  The address formed by the sum of these values is the process break (see brk(2)).  pr_stkbase and pr_stksize are, respectively, the virtual address of the process stack and its size in bytes.  (Each lwp runs on a separate stack; the distinguishing characteristic of the process stack is that the operating system will grow it when necessary.) 

pr_utime, pr_stime, pr_cutime, and pr_cstime are, respectively, the user CPU and system CPU time consumed by the process, and the cumulative user CPU and system CPU time consumed by the process’s children, in seconds and nanoseconds. 

pr_sigtrace and pr_flttrace contain, respectively, the set of signals and the set of hardware faults that are being traced (see PCSTRACE and PCSFAULT). 

pr_sysentry and pr_sysexit contain, respectively, the sets of system calls being traced on entry and exit (see PCSENTRY and PCSEXIT). 

pr_lwp contains the status information for the representative lwp:

typedef struct lwpstatus {
intpr_flags;/∗ flags (see below) ∗/
id_tpr_lwpid;/∗ specific lwp identifier ∗/
shortpr_why;/∗ reason for lwp stop, if stopped ∗/
shortpr_what;/∗ more detailed reason ∗/
shortpr_cursig;/∗ current signal, if any ∗/
siginfo_tpr_info;/∗ info associated with signal or fault ∗/
sigset_tpr_lwppend;/∗ set of signals pending to the lwp ∗/
sigset_tpr_lwphold;/∗ set of signals blocked by the lwp ∗/
struct sigaction pr_action;/∗ signal action for current signal ∗/
stack_tpr_altstack;/∗ alternate signal stack info ∗/
uintptr_tpr_oldcontext;/∗ address of previous ucontext ∗/
shortpr_syscall;/∗ system call number (if in syscall) ∗/
shortpr_nsysarg;/∗ number of arguments to this syscall ∗/
intpr_errno;/∗ errno for failed syscall ∗/
longpr_sysarg[PRSYSARGS];/∗ arguments to this syscall ∗/
longpr_rval1;/∗ primary syscall return value ∗/
longpr_rval2;/∗ second syscall return value, if any ∗/
charpr_clname[PRCLSZ];/∗ scheduling class name ∗/
timestruc_tpr_tstamp;/∗ real-time time stamp of stop ∗/
u_longpr_instr;/∗ current instruction ∗/
prgregset_tpr_reg;/∗ general registers ∗/
prfpregset_tpr_fpreg;/∗ floating-point registers ∗/
} lwpstatus_t;

pr_flags is a bit-mask holding the following lwp flags.  For convenience, it also contains the process flags, described previously. 

PR_STOPPED
lwp is stopped.

PR_ISTOP lwp is stopped on an event of interest (see PCSTOP). 

PR_DSTOP lwp has a stop directive in effect (see PCSTOP). 

PR_STEP lwp has a single-step directive in effect (see PCRUN). 

PR_ASLEEP lwp is in an interruptible sleep within a system call. 

PR_PCINVAL
lwp’s current instruction (pr_instr) is undefined. 

PR_ASLWP this is the asynchronous signal lwp for the process. 

PR_AGENT this is the /proc agent lwp for the process. 

pr_lwpid names the specific lwp. 

pr_why and pr_what together describe, for a stopped lwp, the reason for the stop.  Possible values of pr_why and the associated pr_what are:

PR_REQUESTED indicates that the stop occurred in response to a stop directive, normally because PCSTOP was applied or because another lwp stopped on an event of interest and the asynchronous-stop flag (see PCSET) was not set for the process.  pr_what is unused in this case. 

PR_SIGNALLED indicates that the lwp stopped on receipt of a signal (see PCSTRACE); pr_what holds the signal number that caused the stop (for a newly-stopped lwp, the same value is in pr_cursig). 

PR_FAULTED indicates that the lwp stopped on incurring a hardware fault (see PCSFAULT); pr_what holds the fault number that caused the stop. 

PR_SYSENTRY and PR_SYSEXIT indicate a stop on entry to or exit from a system call (see PCSENTRY and PCSEXIT); pr_what holds the system call number. 

PR_JOBCONTROL indicates that the lwp stopped due to the default action of a job control stop signal (see sigaction(2)); pr_what holds the stopping signal number. 

PR_SUSPENDED indicates that the lwp stopped due to internal synchronization of lwps within the process.  pr_what is unused in this case. 

pr_cursig names the current signal, that is, the next signal to be delivered to the lwp, if any.  pr_info, when the lwp is in a PR_SIGNALLED or PR_FAULTED stop, contains additional information pertinent to the particular signal or fault (see <sys/siginfo.h>). 

pr_lwppend identifies any synchronous or directed signals pending for the lwp.  pr_lwphold identifies those signals whose delivery is being blocked by the lwp (the signal mask). 

pr_action contains the signal action information pertaining to the current signal (see sigaction(2)); it is undefined if pr_cursig is zero.  pr_altstack contains the alternate signal stack information for the lwp (see sigaltstack(2)). 

pr_oldcontext, if not zero, contains the address on the lwp stack of a ucontext structure describing the previous user-level context (see ucontext(5)).  It is non-zero only if the lwp is executing in the context of a signal handler. 

pr_syscall is the number of the system call, if any, being executed by the lwp; it is non-zero if and only if the lwp is stopped on PR_SYSENTRY or PR_SYSEXIT, or is asleep within a system call ( PR_ASLEEP is set).  If pr_syscall is non-zero, pr_nsysarg is the number of arguments to the system call and pr_sysarg contains the actual arguments. 

pr_rval1, pr_rval2, and pr_errno are defined only if the lwp is stopped on PR_SYSEXIT or if the PR_VFORKP flag is set.  If pr_errno is zero, pr_rval1 and pr_rval2 contain the return values from the system call.  Otherwise, pr_errno contains the error number for the failing system call (see <sys/errno.h>). 

pr_clname contains the name of the lwp’s scheduling class. 

pr_tstamp, if the lwp is stopped, contains a time stamp marking when the lwp stopped, in real time seconds and nanoseconds since an arbitrary time in the past. 

pr_instr contains the machine instruction to which the lwp’s program counter refers.  The amount of data retrieved from the process is machine-dependent.  On SPARC based machines, it is a 32-bit word.  On x86 based machines, it is a single byte.  In general, the size is that of the machine’s smallest instruction.  If PR_PCINVAL is set, pr_instr is undefined; this occurs whenever the lwp is not stopped or when the program counter refers to an invalid virtual address. 

pr_reg is an array holding the contents of a stopped lwp’s general registers. 

On SPARC based machines the predefined constants R_G0 ... R_G7, R_O0 ... R_O7, R_L0 ... R_L7, R_I0 ... R_I7, R_PSR, R_PC, R_nPC, R_Y, R_WIM, and R_TBR can be used as indices to refer to the corresponding registers; previous register windows can be read from their overflow locations on the stack (however, see the gwindows file in the /proc/pid/lwp/lwpid subdirectory). 

On x86 based machines, the predefined constants SS, UESP, EFL, CS, EIP, ERR, TRAPNO, EAX, ECX, EDX, EBX, ESP, EBP, ESI, EDI, DS, ES, FS, and GS can be used as indices to refer to the corresponding registers. 

pr_fpreg is a structure holding the contents of the floating-point registers. 

If the lwp is not stopped, all register values are undefined. 

psinfo

Contains miscellaneous information about the process and the representative lwp needed by the ps(1) command.  psinfo is accessible after a process becomes a zombie. The file contains a psinfo structure which contains an embedded lwpsinfo structure for the representative lwp, as follows:

typedef struct psinfo {
intpr_flag;/∗ process flags ∗/
intpr_nlwp;/∗ number of lwps in the process ∗/
pid_tpr_pid;/∗ process id ∗/
pid_tpr_ppid;/∗ process id of parent ∗/
pid_tpr_pgid;/∗ process id of process group leader ∗/
pid_tpr_sid;/∗ session id ∗/
uid_tpr_uid;/∗ real user id ∗/
uid_tpr_euid;/∗ effective user id ∗/
gid_tpr_gid;/∗ real group id ∗/
gid_tpr_egid;/∗ effective group id ∗/
uintptr_tpr_addr;/∗ address of process ∗/
size_tpr_size;/∗ size of process image in Kbytes ∗/
size_tpr_rssize;/∗ resident set size in Kbytes ∗/
dev_tpr_ttydev;/∗ controlling tty device (or PRNODEV) ∗/
u_shortpr_pctcpu;/∗ % of recent cpu time used by all lwps ∗/
u_shortpr_pctmem;/∗ % of system memory used by process ∗/
timestruc_tpr_start;/∗ process start time, from the epoch ∗/
timestruc_tpr_time;/∗ cpu time for this process ∗/
timestruc_tpr_ctime;/∗ cpu time for reaped children ∗/
charpr_fname[PRFNSZ];/∗ name of exec’ed file ∗/
charpr_psargs[PRARGSZ];/∗ initial characters of arg list ∗/
intpr_wstat;/∗ if zombie, the wait() status ∗/
intpr_argc;/∗ initial argument count ∗/
uintptr_tpr_argv;/∗ address of initial argument vector ∗/
uintptr_tpr_envp;/∗ address of initial environment vector ∗/
lwpsinfo_tpr_lwp;/∗ information for representative lwp ∗/
} psinfo_t;

Some of the entries in psinfo, such as pr_flag and pr_addr, refer to internal kernel data structures and should not be expected to retain their meanings across different versions of the operating system. 

pr_pctcpu and pr_pctmem are 16-bit binary fractions in the range 0.0 to 1.0 with the binary point to the right of the high-order bit (1.0 == 0x8000).  pr_pctcpu is the summation over all lwps in the process. 

pr_lwp contains the ps(1) information for the representative lwp.  If the process is a zombie, pr_nlwp and pr_lwp.pr_lwpid are zero and the other fields of pr_lwp are undefined:

typedef struct lwpsinfo {
intpr_flag;/∗ lwp flags ∗/
id_tpr_lwpid;/∗ lwp id ∗/
uintptr_tpr_addr;/∗ internal address of lwp ∗/
uintptr_tpr_wchan;/∗ wait addr for sleeping lwp ∗/
charpr_stype;/∗ synchronization event type ∗/
charpr_state;/∗ numeric lwp state ∗/
charpr_sname;/∗ printable character for pr_state ∗/
charpr_nice;/∗ nice for cpu usage ∗/
shortpr_syscall;/∗ system call number (if in syscall) ∗/
charpr_oldpri;/∗ pre-SVR4, low value is high priority ∗/
charpr_cpu;/∗ pre-SVR4, cpu usage for scheduling ∗/
intpr_pri;/∗ priority, high value = high priority ∗/
u_shortpr_pctcpu;/∗ % of recent cpu time used by this lwp ∗/
timestruc_tpr_start;/∗ lwp start time, from the epoch ∗/
timestruc_tpr_time;/∗ cpu time for this lwp ∗/
charpr_clname[PRCLSZ];/∗ scheduling class name ∗/
charpr_name[PRFNSZ];/∗ name of system lwp ∗/
processorid_t pr_onpro;/∗ processor which last ran this lwp ∗/
processorid_t pr_bindpro;/∗ processor to which lwp is bound ∗/
psetid_tpr_bindpset;/∗ processor set to which lwp is bound ∗/
} lwpsinfo_t;

Some of the entries in lwpsinfo, such as pr_flag, pr_addr, pr_wchan, pr_stype, pr_state, and pr_name, refer to internal kernel data structures and should not be expected to retain their meanings across different versions of the operating system. 

pr_pctcpu is a 16-bit binary fraction, as described above.  It represents the CPU time used by the specific lwp.  On a multi-processor machine, the maximum value is 1/N, where N is the number of CPUs. 

cred

Contains a description of the credentials associated with the process:

typedef struct prcred {
uid_tpr_euid;/∗ effective user id ∗/
uid_tpr_ruid;/∗ real user id ∗/
uid_tpr_suid;/∗ saved user id (from exec) ∗/
gid_tpr_egid;/∗ effective group id ∗/
gid_tpr_rgid;/∗ real group id ∗/
gid_tpr_sgid;/∗ saved group id (from exec) ∗/
intpr_ngroups;/∗ number of supplementary groups ∗/
gid_tpr_groups[1];/∗ array of supplementary groups ∗/
} prcred_t;

The array of associated supplementary groups in pr_groups is of variable length; the cred file contains all of the supplementary groups.  pr_ngroups indicates the number of supplementary groups.  (See also the PCSCRED control operation.) 

sigact

Contains an array of sigaction structures describing the current dispositions of all signals associated with the traced process (see sigaction(2)).  Signal numbers are displaced by 1 from array indices, so that the action for signal number n appears in position n-1 of the array. 

auxv

Contains the initial values of the process’s aux vector in an array of auxv_t structures (see <sys/auxv.h>).  The values are those that were passed by the operating system as startup information to the dynamic linker. 

ldt

This file exists only on x86 based machines.  It is non-empty only if the process has established a local descriptor table (LDT).  If non-empty, the file contains the array of currently active LDT entries in an array of elements of type struct ssd, defined in <sys/sysi86.h>, one element for each active LDT entry. 

map

Contains information about the virtual address map of the process.  The file contains an array of prmap structures, each of which describes a contiguous virtual address region in the address space of the traced process:

typedef struct prmap {
uintptr_tpr_vaddr;/∗ virtual address of mapping ∗/
size_tpr_size;/∗ size of mapping in bytes ∗/
charpr_mapname[PRMAPSZ];/∗ name in /proc/pid/object ∗/
offset_tpr_offset;/∗ offset into mapped object, if any ∗/
intpr_mflags;/∗ protection and attribute flags ∗/
intpr_pagesize;/∗ pagesize for this mapping in bytes ∗/
} prmap_t;

pr_vaddr is the virtual address of the mapping within the traced process and pr_size is its size in bytes.  pr_mapname, if it does not contain a null string, contains the name of a file in the object directory (see below) that can be opened read-only to obtain a file descriptor for the mapped file associated with the mapping.  This enables a debugger to find object file symbol tables without having to know the real path names of the executable file and shared libraries of the process.  pr_offset is the 64-bit offset within the mapped file (if any) to which the virtual address is mapped. 

pr_mflags is a bit-mask of protection and attribute flags:

MA_READ mapping is readable by the traced process. 

MA_WRITE mapping is writable by the traced process. 

MA_EXEC mapping is executable by the traced process. 

MA_SHARED mapping changes are shared by the mapped object. 

A contiguous area of the address space having the same underlying mapped object may appear as multiple mappings due to varying read, write, and execute attributes.  The underlying mapped object does not change over the range of a single mapping.  An I/O operation to a mapping marked MA_SHARED fails if applied at a virtual address not corresponding to a valid page in the underlying mapped object.  A write to a MA_SHARED mapping that is not marked MA_WRITE fails.  Reads and writes to private mappings always succeed.  Reads and writes to unmapped addresses fail. 

pr_pagesize is the page size for the mapping, currently always the system pagesize. 

rmap

Contains information about the reserved address ranges of the process.  The file contains an array of prmap structures, as defined above for the map file.  Each structure describes a contiguous virtual address region in the address space of the traced process that is reserved by the system in the sense that an mmap(2) system call that does not specify MAP_FIXED will not use any part of it for the new mapping.  Examples of such reservations include the address ranges reserved for the process stack and the individual thread stacks of a multi-threaded process. 

cwd

A symbolic link to the process’s current working directory (see chdir(2)).  A readlink(2) of /proc/pid/cwd yields a null string.  However, it can be opened, listed, and searched as a directory and can be the target of chdir(2). 

root

A symbolic link to the process’s root directory.  /proc/pid/root can differ from the system root directory if the process or one of its ancestors executed chroot(2) as super-user.  It has the same semantics as /proc/pid/cwd. 

fd

A directory containing references to the open files of the process.  Each entry is a decimal number corresponding to an open file descriptor in the process. 

If an entry refers to a regular file, it can be opened with normal file system semantics but, to ensure that the controlling process cannot gain greater access than the controlled process, with no file access modes other than its read/write open modes in the controlled process.  If an entry refers to a directory, it appears as a symbolic link and can be accessed with the same semantics as /proc/pid/cwd.  An attempt to open any other type of entry fails with EACCES. 

object

A directory containing read-only files with names corresponding to the pr_mapname entries in the map and pagedata files.  Opening such a file yields a file descriptor for the underlying mapped file associated with an address-space mapping in the process.  The file name a.out appears in the directory as an alias for the process’s executable file. 

The object directory makes it possible for a controlling process to gain access to the object file and any shared libraries (and consequently the symbol tables) without having to know the actual path names of the executable files. 

pagedata

Opening the page data file enables tracking of address space references and modifications on a per-page basis. 

A read(2) of the page data file descriptor returns structured page data and atomically clears the page data maintained for the file by the system.  That is to say, each read returns data collected since the last read; the first read returns data collected since the file was opened.  When the call completes, the read buffer contains the following structure as its header and thereafter contains a number of section header structures and associated byte arrays that must be accessed by walking linearly through the buffer. 

typedef struct prpageheader {
timestruc_tpr_tstamp;/∗ real time stamp, time of read() ∗/
longpr_nmap;/∗ number of address space mappings ∗/
longpr_npage;/∗ total number of pages ∗/
} prpageheader_t;

The header is followed by pr_nmap prasmap structures and associated data arrays.  The prasmap structure contains at least the following elements:

typedef struct prasmap {
uintptr_tpr_vaddr;/∗ virtual address of mapping ∗/
size_tpr_npage;/∗ number of pages in mapping ∗/
charpr_mapname[PRMAPSZ];/∗ name in /proc/pid/object ∗/
offset_tpr_offset;/∗ offset into mapped object, if any ∗/
intpr_mflags;/∗ protection and attribute flags ∗/
intpr_pagesize;/∗ pagesize for this mapping in bytes ∗/
} prasmap_t;

Each section header is followed by pr_npage bytes, one byte for each page in the mapping, plus 0-7 null bytes at the end so that the next prasmap structure begins on an eight-byte aligned boundary.  Each data byte may contain these flags:

PG_REFERENCED
page has been referenced.

PG_MODIFIED page has been modified. 

If the read buffer is not large enough to contain all of the page data, the read fails with E2BIG and the page data is not cleared.  The required size of the read buffer can be determined through fstat(2).  Application of lseek(2) to the page data file descriptor is ineffective; every read starts from the beginning of the file.  Closing the page data file descriptor terminates the system overhead associated with collecting the data. 

More than one page data file descriptor for the same process can be opened, up to a system-imposed limit per traced process.  A read of one does not affect the data being collected by the system for the others.  An open of the page data file will fail with ENOMEM if the system-imposed limit would be exceeded. 

watch

Contains an array of prwatch structures, one for each watched area established by the PCWATCH control operation.  See PCWATCH for details. 

usage

Contains process usage information described by a prusage structure which contains at least the following fields:

typedef struct prusage {
id_tpr_lwpid;/∗ lwp id.  0: process or defunct ∗/
intpr_count;/∗ number of contributing lwps ∗/
timestruc_tpr_tstamp;/∗ real time stamp, time of read() ∗/
timestruc_tpr_create;/∗ process/lwp creation time stamp ∗/
timestruc_tpr_term;/∗ process/lwp termination time stamp ∗/
timestruc_tpr_rtime;/∗ total lwp real (elapsed) time ∗/
timestruc_tpr_utime;/∗ user level CPU time ∗/
timestruc_tpr_stime;/∗ system call CPU time ∗/
timestruc_tpr_ttime;/∗ other system trap CPU time ∗/
timestruc_tpr_tftime;/∗ text page fault sleep time ∗/
timestruc_tpr_dftime;/∗ data page fault sleep time ∗/
timestruc_tpr_kftime;/∗ kernel page fault sleep time ∗/
timestruc_tpr_ltime;/∗ user lock wait sleep time ∗/
timestruc_tpr_slptime;/∗ all other sleep time ∗/
timestruc_tpr_wtime;/∗ wait-cpu (latency) time ∗/
timestruc_tpr_stoptime;/∗ stopped time ∗/
u_longpr_minf;/∗ minor page faults ∗/
u_longpr_majf;/∗ major page faults ∗/
u_longpr_nswap;/∗ swaps ∗/
u_longpr_inblk;/∗ input blocks ∗/
u_longpr_oublk;/∗ output blocks ∗/
u_longpr_msnd;/∗ messages sent ∗/
u_longpr_mrcv;/∗ messages received ∗/
u_longpr_sigs;/∗ signals received ∗/
u_longpr_vctx;/∗ voluntary context switches ∗/
u_longpr_ictx;/∗ involuntary context switches ∗/
u_longpr_sysc;/∗ system calls ∗/
u_longpr_ioch;/∗ chars read and written ∗/
} prusage_t;

If microstate accounting has not been enabled for the process (see the PR_MSACCT flag for the PCSET operation, below), the usage file contains only an estimate of times spent in the various states.  The usage file is accessible after a process becomes a zombie.

lstatus

Contains a prheader structure followed by an array of lwpstatus structures, one for each lwp in the process (see also /proc/pid/lwp/lwpid/lwpstatus, below).  The prheader structure describes the number and size of the array entries that follow. 

typedef struct prheader {
intpr_nent;/∗ number of entries ∗/
intpr_entsize;/∗ size of each entry, in bytes ∗/
} prheader_t;

The lwpstatus structure may grow by the addition of elements at the end in future releases of the system.  Programs must use pr_entsize in the file header to index through the array.  These comments apply to all /proc files that include a prheader structure (lpsinfo and lusage, below). 

lpsinfo

Contains a prheader structure followed by an array of lwpsinfo structures, one for each lwp in the process.  (See also /proc/pid/lwp/lwpid/lwpsinfo, below.) 

lusage

Contains a prheader structure followed by an array of prusage structures, one for each lwp in the process plus an additional element at the beginning that contains the summation over all defunct lwps (lwps that once existed but no longer exist in the process).  Excluding the pr_lwpid, pr_tstamp, pr_create, and pr_term entries, the entry-by-entry summation over all these structures is the definition of the process usage information obtained from the usage file.  (See also /proc/pid/lwp/lwpid/lwpusage, below.) 

lwp

A directory containing entries each of which names an lwp within the process.  These entries are themselves directories containing additional files as described below. 

STRUCTURE OF /proc/pid/lwp/lwpid

A given directory /proc/pid/lwp/lwpid contains the following entries:

lwpctl

Write-only control file.  The messages written to this file affect the specific lwp rather than the representative lwp, as is the case for the process’s ctl file. 

lwpstatus

lwp-specific state information.  This file contains the lwpstatus structure for the specific lwp as described above for the representative lwp in the process’s status file. 

lwpsinfo

lwp-specific ps(1) information.  This file contains the lwpsinfo structure for the specific lwp as described above for the representative lwp in the process’s psinfo file. 

lwpusage

This file contains the prusage structure for the specific lwp as described above for the process’s usage file. 

gwindows

This file exists only on SPARC based machines.  If it is non-empty, it contains a gwindows_t structure, defined in <sys/regset.h>, with the values of those SPARC register windows that could not be stored on the stack when the lwp stopped.  Conditions under which register windows are not stored on the stack are: the stack pointer refers to nonexistent process memory or the stack pointer is improperly aligned.  If the lwp is not stopped or if there are no register windows that could not be stored on the stack, the file is empty (the usual case). 

xregs

Extra state registers.  The extra state register set is architecture dependent; this file is empty if the system does not support extra state registers.  If the file is non-empty, it contains an architecture dependent structure of type prxregset_t, defined in <procfs.h>, with the values of the lwp’s extra state registers.  If the lwp is not stopped, all register values are undefined.  See also the PCSXREG control operation, below. 

CONTROL MESSAGES

Process state changes are effected through messages written to a process’s ctl file or to an individual lwp’s lwpctl file.  All control messages consist of a long that names the specific operation followed by additional data containing the operand, if any. 

Multiple control messages may be combined in a single write(2) (or writev(2)) to a control file, but no partial writes are permitted.  That is, each control message, operation code plus operand, if any, must be presented in its entirety to the write(2) and not in pieces over several system calls.  If a control operation fails, no subsequent operations contained in the same write(2) are attempted. 

Descriptions of the allowable control messages follow.  In all cases, writing a message to a control file for a process or lwp that has terminated elicits the error ENOENT. 

PCSTOP    PCDSTOP PCWSTOP PCTWSTOP

When applied to the process control file, PCSTOP directs all lwps to stop and waits for them to stop, PCDSTOP directs all lwps to stop without waiting for them to stop, and PCWSTOP simply waits for all lwps to stop.  When applied to an lwp control file, PCSTOP directs the specific lwp to stop and waits until it has stopped, PCDSTOP directs the specific lwp to stop without waiting for it to stop, and PCWSTOP simply waits for the specific lwp to stop.  When applied to an lwp control file, PCSTOP and PCWSTOP complete when the lwp stops on an event of interest, immediately if already so stopped; when applied to the process control file, they complete when every lwp has stopped either on an event of interest or on a PR_SUSPENDED stop. 

PCTWSTOP is identical to PCWSTOP except that it enables the operation to time out, to avoid waiting forever for a process or lwp that may never stop on an event of interest.  PCTWSTOP takes a long operand specifying a number of milliseconds; the wait will terminate successfully after the specified number of milliseconds even if the process or lwp has not stopped; a timeout value of zero makes the operation identical to PCWSTOP.

An “event of interest” is either a PR_REQUESTED stop or a stop that has been specified in the process’s tracing flags (set by PCSTRACE, PCSFAULT, PCSENTRY, and PCSEXIT).  PR_JOBCONTROL and PR_SUSPENDED stops are specifically not events of interest.  (An lwp may stop twice due to a stop signal, first showing PR_SIGNALLED if the signal is traced and again showing PR_JOBCONTROL if the lwp is set running without clearing the signal.)  If PCSTOP or PCDSTOP is applied to an lwp that is stopped, but not on an event of interest, the stop directive takes effect when the lwp is restarted by the competing mechanism.  At that time, the lwp enters a PR_REQUESTED stop before executing any user-level code. 

A write of a control message that blocks is interruptible by a signal so that, for example, an alarm(2) can be set to avoid waiting forever for a process or lwp that may never stop on an event of interest.  If PCSTOP is interrupted, the lwp stop directives remain in effect even though the write(2) returns an error.  (Use of PCTWSTOP with a non-zero timeout is recommended over PCWSTOP with an alarm(2).) 

A system process (indicated by the PR_ISSYS flag) never executes at user level, has no user-level address space visible through /proc, and cannot be stopped.  Applying one of these operations to a system process or any of its lwps elicits the error EBUSY. 

PCRUN

Make an lwp runnable again after a stop.  This operation takes a long operand containing zero or more of the following flags:

PRCSIG clears the current signal, if any (see PCCSIG). 

PRCFAULT clears the current fault, if any (see PCCFAULT). 

PRSTEP directs the lwp to execute a single machine instruction.  On completion of the instruction, a trace trap occurs.  If FLTTRACE is being traced, the lwp stops; otherwise, it is sent SIGTRAP.  If SIGTRAP is being traced and is not blocked, the lwp stops.  When the lwp stops on an event of interest, the single-step directive is cancelled, even if the stop occurs before the instruction is executed.  This operation requires hardware and operating system support and may not be implemented on all processors.  It is implemented on SPARC and x86 based machines. 

PRSABORT is meaningful only if the lwp is in a PR_SYSENTRY stop or is marked PR_ASLEEP; it instructs the lwp to abort execution of the system call (see PCSENTRY and PCSEXIT). 

PRSTOP directs the lwp to stop again as soon as possible after resuming execution (see PCDSTOP).  In particular, if the lwp is stopped on PR_SIGNALLED or PR_FAULTED, the next stop will show PR_REQUESTED, no other stop will have intervened, and the lwp will not have executed any user-level code. 

When applied to an lwp control file, PCRUN clears any outstanding directed-stop request and makes the specific lwp runnable.  The operation fails with EBUSY if the specific lwp is not stopped on an event of interest or has not been directed to stop or if the agent lwp exists and this is not the agent lwp (see PCAGENT). 

When applied to the process control file, a representative lwp is chosen for the operation as described for /proc/pid/status.  The operation fails with EBUSY if the representative lwp is not stopped on an event of interest or has not been directed to stop or if the agent lwp exists.  If PRSTEP or PRSTOP was requested, the representative lwp is made runnable and its outstanding directed-stop request is cleared; otherwise all outstanding directed-stop requests are cleared and, if it was stopped on an event of interest, the representative lwp is marked PR_REQUESTED.  If, as a consequence, all lwps are in the PR_REQUESTED or PR_SUSPENDED stop state, all lwps showing PR_REQUESTED are made runnable. 

PCSTRACE

Define a set of signals to be traced in the process.  The receipt of one of these signals by an lwp causes the lwp to stop.  The set of signals is defined using an operand sigset_t contained in the control message.  Receipt of SIGKILL cannot be traced; if specified, it is silently ignored. 

If a signal that is included in an lwp’s held signal set (the signal mask) is sent to the lwp, the signal is not received and does not cause a stop until it is removed from the held signal set, either by the lwp itself or by setting the held signal set with PCSHOLD. 

PCCSIG

The current signal, if any, is cleared from the specific or representative lwp. 

PCSSIG

The current signal and its associated signal information for the specific or representative lwp are set according to the contents of the operand siginfo structure (see <sys/siginfo.h>).  If the specified signal number is zero, the current signal is cleared.  The semantics of this operation are different from those of kill(2) in that the signal is delivered to the lwp immediately after execution is resumed (even if it is being blocked) and an additional PR_SIGNALLED stop does not intervene even if the signal is traced.  Setting the current signal to SIGKILL terminates the process immediately. 

PCKILL

If applied to the process control file, a signal is sent to the process with semantics identical to those of kill(2).  If applied to an lwp control file, a directed signal is sent to the specific lwp.  The signal is named in a long operand contained in the message.  Sending SIGKILL terminates the process immediately. 

PCUNKILL

A signal is deleted, that is, it is removed from the set of pending signals.  If applied to the process control file, the signal is deleted from the process’s pending signals.  If applied to an lwp control file, the signal is deleted from the lwp’s pending signals.  The current signal (if any) is unaffected.  The signal is named in a long operand in the control message.  It is an error (EINVAL) to attempt to delete SIGKILL. 

PCSHOLD

Set the set of held signals for the specific or representative lwp (signals whose delivery will be blocked if sent to the lwp).  The set of signals is specified with a sigset_t operand.  SIGKILL and SIGSTOP cannot be held; if specified, they are silently ignored. 

PCSFAULT

Define a set of hardware faults to be traced in the process.  On incurring one of these faults, an lwp stops.  The set is defined via the operand fltset_t structure.  Fault names are defined in <sys/fault.h> and include the following.  Some of these may not occur on all processors; there may be processor-specific faults in addition to these. 

FLTILL illegal instruction

FLTPRIV privileged instruction

FLTBPT breakpoint trap

FLTTRACE trace trap (single-step)

FLTWATCH watchpoint trap

FLTACCESS memory access fault (bus error)

FLTBOUNDS memory bounds violation

FLTIOVF integer overflow

FLTIZDIV integer zero divide

FLTFPE floating-point exception

FLTSTACK unrecoverable stack fault

FLTPAGE recoverable page fault

When not traced, a fault normally results in the posting of a signal to the lwp that incurred the fault.  If an lwp stops on a fault, the signal is posted to the lwp when execution is resumed unless the fault is cleared by PCCFAULT or by the PRCFAULT option of PCRUN.  FLTPAGE is an exception; no signal is posted.  The pr_info field in the lwpstatus structure identifies the signal to be sent and contains machine-specific information about the fault. 

PCCFAULT

The current fault, if any, is cleared; the associated signal will not be sent to the specific or representative lwp. 

PCSENTRY PCSEXIT

These control operations instruct the process’s lwps to stop on entry to or exit from specified system calls.  The set of system calls to be traced is defined via an operand sysset_t structure. 

When entry to a system call is being traced, an lwp stops after having begun the call to the system but before the system call arguments have been fetched from the lwp.  When exit from a system call is being traced, an lwp stops on completion of the system call just prior to checking for signals and returning to user level.  At this point, all return values have been stored into the lwp’s registers. 

If an lwp is stopped on entry to a system call (PR_SYSENTRY) or when sleeping in an interruptible system call (PR_ASLEEP is set), it may be instructed to go directly to system call exit by specifying the PRSABORT flag in a PCRUN control message.  Unless exit from the system call is being traced, the lwp returns to user level showing EINTR. 

PCWATCH

Set or clear a watched area in the controlled process from a prwatch structure operand:

typedef struct prwatch {
uintptr_tpr_vaddr;/∗ virtual address of watched area ∗/
size_tpr_size;/∗ size of watched area in bytes ∗/
intpr_wflags;/∗ watch type flags ∗/
} prwatch_t;

pr_vaddr specifies the virtual address of an area of memory to be watched in the controlled process.  pr_size specifies the size of the area, in bytes.  pr_wflags specifies the type of memory access to be monitored as a bit-mask of the following flags:

WA_READ read access

WA_WRITE write access

WA_EXEC execution access

WA_TRAPAFTER
trap after the instruction completes

If pr_wflags is non-empty, a watched area is established for the virtual address range specified by pr_vaddr and pr_size.  If pr_wflags is empty, any previously-established watched area starting at the specified virtual address is cleared; pr_size is ignored. 

A watchpoint is triggered when an lwp in the traced process makes a memory reference that covers at least one byte of a watched area and the memory reference is as specified in pr_wflags.  When an lwp triggers a watchpoint, it incurs a watchpoint trap.  If FLTWATCH is being traced, the lwp stops; otherwise, it is sent a SIGTRAP signal; if SIGTRAP is being traced and is not blocked, the lwp stops. 

The watchpoint trap occurs before the instruction completes unless WA_TRAPAFTER was specified, in which case it occurs after the instruction completes.  If it occurs before completion, the memory is not modified.  If it occurs after completion, the memory is modified (if the access is a write access). 

pr_info in the lwpstatus structure contains information pertinent to the watchpoint trap.  In particular, the si_addr field contains the virtual address of the memory reference that triggered the watchpoint, and the si_code field contains one of TRAP_RWATCH, TRAP_WWATCH, or TRAP_XWATCH, indicating read, write, or execute access, respectively.  The si_trapafter field is zero unless WA_TRAPAFTER is in effect for this watched area; non-zero indicates that the current instruction is not the instruction that incurred the watchpoint trap.  The si_pc field contains the virtual address of the instruction that incurred the trap. 

A watchpoint trap may be triggered while executing a system call that makes reference to the traced process’s memory.  The lwp that is executing the system call incurs the watchpoint trap while still in the system call.  If it stops as a result, the lwpstatus structure contains the system call number and its arguments.  If the lwp does not stop, or if it is set running again without clearing the signal or fault, the system call fails with EFAULT.  If WA_TRAPAFTER was specified, the memory reference will have completed and the memory will have been modified (if the access was a write access) when the watchpoint trap occurs. 

If more than one of WA_READ, WA_WRITE, and WA_EXEC is specified for a watched area, and a single instruction incurs more than one of the specified types, only one is reported when the watchpoint trap occurs.  The precedence is WA_EXEC, WA_READ, WA_WRITE ( WA_EXEC and WA_READ take precedence over WA_WRITE), unless WA_TRAPAFTER was specified, in which case it is WA_WRITE, WA_READ, WA_EXEC ( WA_WRITE takes precedence). 

PCWATCH fails with EINVAL if an attempt is made to specify overlapping watched areas or if pr_wflags contains flags other than those specified above.  It fails with ENOMEM if an attempt is made to establish more watched areas than the system can support (the system can support thousands). 

The child of a vfork(2) borrows the parent’s address space.  When a vfork(2) is executed by a traced process, all watched areas established for the parent are suspended until the child terminates or performs an exec(2).  Any watched areas established independently in the child are cancelled when the parent resumes after the child’s termination or exec(2).  PCWATCH fails with EBUSY if applied to the parent of a vfork(2) before the child has terminated or performed an exec(2).  The PR_VFORKP flag is set in the pstatus structure for such a parent process. 

Certain accesses of the traced process’s address space by the operating system are immune to watchpoints.  The initial construction of a signal stack frame when a signal is delivered to an lwp will not trigger a watchpoint trap even if the new frame covers watched areas of the stack.  Once the signal handler is entered, watchpoint traps occur normally.  On SPARC based machines, register window overflow and underflow will not trigger watchpoint traps, even if the register window save areas cover watched areas of the stack. 

Watched areas are not inherited by child processes, even if the traced process’s inherit-on-fork mode, PR_FORK, is set (see PCSET, below).  All watched areas are cancelled when the traced process performs a successful exec(2). 

    PCSET   PCUNSET

PCSET sets one or more modes of operation for the traced process.  PCUNSET unsets these modes.  The modes to be set or unset are specified by flags in an operand long in the control message:

PR_FORK (inherit-on-fork): When set, the process’s tracing flags and its inherit-on-fork mode are inherited by the child of a fork(2), fork1(2), or vfork(2).  When unset, child processes start with all tracing flags cleared. 

PR_RLC (run-on-last-close): When set and the last writable /proc file descriptor referring to the traced process or any of its lwps is closed, all of the process’s tracing flags and watched areas are cleared, any outstanding stop directives are canceled, and if any lwps are stopped on events of interest, they are set running as though PCRUN had been applied to them.  When unset, the process’s tracing flags and watched areas are retained and lwps are not set running on last close. 

PR_KLC (kill-on-last-close): When set and the last writable /proc file descriptor referring to the traced process or any of its lwps is closed, the process is terminated with SIGKILL. 

PR_ASYNC (asynchronous-stop): When set, a stop on an event of interest by one lwp does not directly affect any other lwp in the process.  When unset and an lwp stops on an event of interest other than PR_REQUESTED, all other lwps in the process are directed to stop. 

PR_MSACCT (microstate accounting): When set, microstate accounting is enabled for the process.  This allows the usage file to contain accurate values for the times the lwps spent in their various processing states.  When unset (the default), the overhead of microstate accounting is avoided and the usage file can only contain an estimate of times spent in the various states. 

PR_MSFORK (inherit microstate accounting): When set, and microstate accounting is enabled for the process, microstate accounting will be enabled for future child processes.  When unset, child processes start with microstate accounting disabled. 

PR_BPTADJ (breakpoint trap pc adjustment): On x86 based machines, a breakpoint trap leaves the program counter (the EIP) referring to the breakpointed instruction plus one byte.  When PR_BPTADJ is set, the system will adjust the program counter back to the location of the breakpointed instruction when the lwp stops on a breakpoint.  This flag has no effect on SPARC based machines, where breakpoint traps leave the program counter referring to the breakpointed instruction. 

PR_PTRACE (ptrace-compatibility): When set, a stop on an event of interest by the traced process is reported to the parent of the traced process via wait(2), SIGTRAP is sent to the traced process when it executes a successful exec(2), setuid/setgid flags are not honored for execs performed by the traced process, any exec of an object file that the traced process cannot read fails, and the process dies when its parent dies.  This mode is deprecated; it is provided only to allow ptrace(2) to be implemented as a library function using /proc. 

It is an error (EINVAL) to specify flags other than those described above or to apply these operations to a system process.  The current modes are reported in the pr_flags field of /proc/pid/status and /proc/pid/lwp/lwp/lwpstatus. 

PCSREG

Set the general registers for the specific or representative lwp according to the operand prgregset_t structure. 

On SPARC based systems, only certain bits of the processor-status register (R_PS) can be modified by PCSREG: these include only the condition-code bits.  Other privileged registers cannot be modified at all. 

On x86 based systems, only certain bits of the flags register (EFL) can be modified by PCSREG: these include the condition codes, direction-bit, and overflow-bit. 

PCSREG fails with EBUSY if the lwp is not stopped on an event of interest. 

PCSVADDR

Set the address at which execution will resume for the specific or representative lwp from the operand long.  On SPARC based systems, both %pc and %npc are set, with %npc set to the instruction following the virtual address.  On x86 based systems, only %eip is set.  PCSVADDR fails with EBUSY if the lwp is not stopped on an event of interest. 

PCSFPREG

Set the floating-point registers for the specific or representative lwp according to the operand prfpregset_t structure.  An error (EINVAL) is returned if the system does not support floating-point operations (no floating-point hardware and the system does not emulate floating-point machine instructions).  PCSFPREG fails with EBUSY if the lwp is not stopped on an event of interest. 

PCSXREG

Set the extra state registers for the specific or representative lwp according to the architecture-dependent operand prxregset_t structure.  An error (EINVAL) is returned if the system does not support extra state registers.  PCSXREG fails with EBUSY if the lwp is not stopped on an event of interest. 

PCAGENT

Create an agent lwp in the controlled process with register values from the operand prgregset_t structure (see PCSREG, above).  The agent lwp is created in the stopped state showing PR_REQUESTED and with its held signal set (the signal mask) having all signals except SIGKILL and SIGSTOP blocked. 

The PCAGENT operation fails with EBUSY unless the process is fully stopped via /proc, that is, unless all of the lwps in the process are stopped either on events of interest or on PR_SUSPENDED, or are stopped on PR_JOBCONTROL and have been directed to stop via PCDSTOP.   It fails with EBUSY if an agent lwp already exists.  It fails with ENOMEM if system resources for creating new lwps have been exhausted. 

Any PCRUN operation applied to the process control file or to the control file of an lwp other than the agent lwp fails with EBUSY as long as the agent lwp exists.  The agent lwp must be caused to terminate by executing the _lwp_exit(2) system call before the process can be restarted. 

Once the agent lwp is created, its lwp-ID can be found by reading the process status file.  To facilitate opening the agent lwp’s control and status files, the directory name /propc/pid/lwp/agent is accepted for lookup operations as an invisible alias for /proc/pid/lwp/lwpid, lwpid being the lwp-ID of the agent lwp (invisible in the sense that the name “agent” does not appear in a directory listing of /proc/pid/lwp obtained from ls(1), getdents(2), or readdir(3C)). 

The purpose of the agent lwp is to perform operations in the controlled process on behalf of the controlling process: to gather information not directly available via /proc files, or in general to make the process change state in ways not directly available via /proc control operations.  To make use of an agent lwp, the controlling process must be capable of making it execute system calls (specifically, the _lwp_exit(2) system call).  The register values given to the agent lwp on creation are typically the registers of the representative lwp, so that the agent lwp can use its stack. 

The agent lwp is not allowed to execute any variation of the fork(2), exec(2), or _lwp_create(2) system calls.  Attempts to do so yield ENOTSUP to the agent lwp. 

   PCREAD   PCWRITE

Read or write the target process’s address space via a priovec structure operand:

typedef struct priovec {
void∗pio_base;/∗ buffer in controlling process ∗/
size_tpio_len;/∗ size of read/write request in bytes ∗/
off_tpio_offset;/∗ virtual address in target process ∗/
} priovec_t;

These operations have the same effect as pread(2) and pwrite(2), respectively, of the target process’s address space file.  The difference is that more than one PCREAD or PCWRITE control operation can be written to the control file at once, and they can be interspersed with other control operations in a single write to the control file.  This is useful, for example, when planting many breakpoint instructions in the process’s address space, or when stepping over a breakpointed instruction.  Unlike pread(2) and pwrite(2), no provision is made for partial reads or writes; if the operation cannot be performed completely, it fails with EIO. 

PCNICE

The traced process’s nice(2) value is incremented by the amount in the operand long.  Only the super-user may better a process’s priority in this way, but any user may lower the priority.  This operation is not meaningful for all scheduling classes. 

PCSCRED

Set the target process credentials to the values contained in the prcred_t structure operand (see /proc/pid/cred).  The effective, real, and saved user-IDs and group-IDs of the target process are set.  The target process’s supplementary groups are not changed; the pr_ngroups and pr_groups members of the structure operand are ignored.  Only the super-user may perform this operation; for all others it fails with EPERM. 

PROGRAMMING NOTES

For security reasons, except for the psinfo, usage, lpsinfo, lusage, lwpsinfo, and lwpusage files, which are world-readable, and except for the super-user, an open of a /proc file fails unless both the user-ID and group-ID of the caller match those of the traced process and the process’s object file is readable by the caller.  Except for the world-readable files just mentioned, files corresponding to setuid and setgid processes can be opened only by the super-user. 

Even if held by the super-user, an open process or lwp file descriptor (other than file descriptors for the world-readable files) becomes invalid if the traced process performs an exec(2) of a setuid/setgid object file or an object file that the traced process cannot read.  Any operation performed on an invalid file descriptor, except close(2), fails with EAGAIN.  In this situation, if any tracing flags are set and the process or any lwp file descriptor is open for writing, the process will have been directed to stop and its run-on-last-close flag will have been set (see PCSET).  This enables a controlling process (if it has permission) to reopen the /proc files to get new valid file descriptors, close the invalid file descriptors, unset the run-on-last-close flag (if desired), and proceed.  Just closing the invalid file descriptors causes the traced process to resume execution with all tracing flags cleared.  Any process not currently open for writing via /proc, but that has left-over tracing flags from a previous open, and that executes a setuid/setgid or unreadable object file, will not be stopped but will have all its tracing flags cleared. 

To wait for one or more of a set of processes or lwps to stop or terminate, /proc file descriptors (other than those obtained by opening the cwd or root directories or by opening files in the fd or object directories) can be used in a poll(2) system call.  When requested and returned, either of the polling events POLLPRI or POLLWRNORM indicates that the process or lwp stopped on an event of interest.  Although they cannot be requested, the polling events POLLHUP, POLLERR, and POLLNVAL may be returned.  POLLHUP indicates that the process or lwp has terminated.  POLLERR indicates that the file descriptor has become invalid.  POLLNVAL is returned immediately if POLLPRI or POLLWRNORM is requested on a file descriptor referring to a system process (see PCSTOP).  The requested events may be empty to wait simply for termination. 

FILES

/proc directory (list of processes)

/proc/pid specific process directory

/proc/self alias for a process’s own directory

/proc/pid/as address space file

/proc/pid/ctl process control file

/proc/pid/status process status

/proc/pid/lstatus array of lwp status structs

/proc/pid/psinfo process ps(1) info

/proc/pid/lpsinfo array of lwp ps(1) info structs

/proc/pid/map address space map

/proc/pid/rmap reserved address map

/proc/pid/cred process credentials

/proc/pid/sigact process signal actions

/proc/pid/auxv process aux vector

/proc/pid/ldt process LDT (x86 only)

/proc/pid/usage process usage

/proc/pid/lusage array of lwp usage structs

/proc/pid/pagedata
process page data

/proc/pid/watch active watchpoints

/proc/pid/cwd symlink to the current working directory

/proc/pid/root symlink to the root directory

/proc/pid/fd directory (list of open files)

/proc/pid/fd/∗ aliases for process’s open files

/proc/pid/object directory (list of mapped files)

/proc/pid/object/a.out alias for process’s executable file

/proc/pid/object/∗
aliases for other mapped files

/proc/pid/lwp directory (list of lwps)

/proc/pid/lwp/lwpid specific lwp directory

/proc/pid/lwp/agent alias for the agent lwp directory

/proc/pid/lwp/lwpid/lwpctl lwp control file

/proc/pid/lwp/lwpid/lwpstatus lwp status

/proc/pid/lwp/lwpid/lwpsinfo lwp ps(1) info

/proc/pid/lwp/lwpid/lwpusage lwp usage

/proc/pid/lwp/lwpid/gwindows register windows (SPARC only)

/proc/pid/lwp/lwpid/xregs extra state registers

SEE ALSO

ls(1), ps(1), _lwp_create(2), _lwp_exit(2), alarm(2), brk(2), chdir(2), chroot(2), close(2), creat(2), dup(2), exec(2), fcntl(2), fork(2), fork1(2), fstat(2), getdents(2), kill(2), lseek(2), mmap(2), nice(2), open(2), poll(2), pread(2), ptrace(2), pwrite(2), read(2), readlink(2), readv(2), sigaction(2), sigaltstack(2), vfork(2), wait(2), write(2), writev(2), readdir(3C), siginfo(5), signal(5), ucontext(5)

DIAGNOSTICS

Errors that can occur in addition to the errors normally associated with file system access:

ENOENT The traced process or lwp has terminated after being opened. 

EIO A write(2) was attempted at an illegal address in the traced process. 

EBUSY PCSTOP, PCDSTOP, PCWSTOP, or PCTWSTOP was applied to a system process; an exclusive open(2) was attempted on a /proc file for a process already open for writing; PCRUN, PCSREG, PCSVADDR, PCSFPREG, or PCSXREG was applied to a process or lwp not stopped on an event of interest; an attempt was made to mount /proc when it was already mounted; PCAGENT was applied to a process that was not fully stopped or that already had an agent lwp. 

EPERM Someone other than the super-user issued the PCSCRED operation; someone other than the super-user attempted to better a process’s priority by applying PCNICE. 

ENOSYS An attempt was made to perform an unsupported operation (such as creat(2), link(2), or unlink(2)) on an entry in /proc. 

EINVAL In general, this means that some invalid argument was supplied to a system call.  A non-exhaustive list of conditions eliciting this error includes: a control message operation code is undefined; an out-of-range signal number was specified with PCSSIG, PCKILL, or PCUNKILL; SIGKILL was specified with PCUNKILL; PCSFPREG was applied on a system that does not support floating-point operations; PCSXREG was applied on a system that does not support extra state registers. 

ENOMEM
The system-imposed limit on the number of page data file descriptors was reached on an open of /proc/pid/pagedata; an attempt was made with PCWATCH to establish more watched areas than the system can support; the PCAGENT operation was issued when the system was out of resources for creating lwps. 

E2BIG Data to be returned in a read(2) of the page data file exceeds the size of the read buffer provided by the caller. 

EINTR A signal was received by the controlling process while waiting for the traced process or lwp to stop via PCSTOP, PCWSTOP, or PCTWSTOP. 

EAGAIN The traced process has performed an exec(2) of a setuid/setgid object file or of an object file that it cannot read; all further operations on the process or lwp file descriptor (except close(2)) elicit this error. 

NOTES

Descriptions of structures in this document include only interesting structure elements, not filler and padding fields, and may show elements out of order for descriptive clarity.  The actual structure definitions are contained in <procfs.h>. 

BUGS

Because the old ioctl(2)-based version of /proc is currently supported for binary compatibility with old applications, the top-level directory for a process, /proc/pid, is not world-readable, but it is world-searchable.  Thus, anyone can open /proc/pid/psinfo even though ls(1) applied to /proc/pid will fail for anyone but the owner or the super-user.  Support for the old ioctl(2)-based version of /proc will be dropped in a future release, at which time the top-level directory for a process will be made world-readable. 

On SPARC based machines, the types gregset_t and fpregset_t defined in <sys/regset.h> are similar to but not the same as the types prgregset_t and prfpregset_t defined in <procfs.h>. 

SunOS 5.6  —  Last change: 13 Feb 1997