NAME

exec: execl, execv, execle, execve, execlp, execvp − execute a file

SYNOPSIS

int execl (path, arg0, arg1, ..., argn, (char ∗)0)
char ∗path, ∗arg0, ∗arg1, ..., ∗argn;

int execv (path, argv)
char ∗path, ∗argv[ ];

int execle (path, arg0, arg1, ..., argn, (char ∗)0, envp)
char ∗path, ∗arg0, ∗arg1, ..., ∗argn, ∗envp[ ];

int execve (path, argv, envp)
char ∗path, ∗argv[ ], ∗envp[ ];

int execlp (file, arg0, arg1, ..., argn, (char ∗)0)
char ∗file, ∗arg0, ∗arg1, ..., ∗argn;

int execvp (file, argv)
char ∗file, ∗argv[ ];

DESCRIPTION

exec in all its forms transforms the calling process into a new process.  The new process is constructed from an ordinary, executable file called the new process file. This file consists of a header [see a.out(4)], a text segment, a data segment, and an optional threadlocal data segment (see thread(2)). The data segment contains an initialized portion and an uninitialized portion (bss).

There can be no return from a successful exec because the calling process is overlaid by the new process. 

Optionally, the new process file may be an interpreter file. An interpreter file begins with a line of the following form:

!#interpreter

When an interpreter file is exec’d, the system execs the specified interpreter, giving it the name of the originally exec’d file as an argument and shifting over the rest of the optional arguments.

When a C program is executed, it is called as follows:

main (argc, argv, envp)
int argc;
char ∗∗argv, ∗∗envp;

where argc is the argument count, argv is an array of character pointers to the arguments themselves, and envp is an array of character pointers to the environment strings.  As indicated, argc is conventionally at least one and the first member of the array points to a string containing the name of the file. 

path points to a path name that identifies the new process file. 

file points to the new process file.  The path prefix for this file is obtained by a search of the directories passed as the environment line "PATH =" [see environ(5)]. The environment is supplied by the shell [see sh(1) and csh(1)].

arg0, arg1, ..., argn are pointers to null-terminated character strings.  These strings constitute the argument list available to the new process.  By convention, at least arg0 must be present and point to a string that is the same as path (or its last component). 

argv is an array of character pointers to null-terminated strings.  These strings constitute the argument list available to the new process.  By convention, argv must have at least one member, and it must point to a string that is the same as path (or its last component).  argv is terminated by a null pointer. 

envp is an array of character pointers to null-terminated strings.  These strings constitute the environment for the new process.  envp is terminated by a null pointer.  For execl and execv, the C run-time start-off routine places a pointer to the environment of the calling process in the global cell:
extern char ∗∗environ;
and it is used to pass the environment of the calling process to the new process.

File descriptors open in the calling process remain open in the new process, except for those whose ­close-on-exec flag is set; see fcntl(2). For those file descriptors that remain open, the file pointer is unchanged.

Signals set to terminate the calling process will be set to terminate the new process.  Signals set to be ignored by the calling process will be set to be ignored by the new process.  Signals set to be caught by the calling process will be set to terminate new process; see signal(2).

For signals set by sigset(2), exec ensures that the new process has the same system signal action for each signal type whose action is SIG_DFL, SIG_IGN, or SIG_HOLD as the calling process.  However, if the action is to catch the signal, then the action is reset to SIG_DFL, and any pending signal for this type is held. 

If the set-user-ID mode bit of the new process file is set [see chmod(2)], exec sets the effective user ID of the new process to the owner ID of the new process file.  Similarly, if the set-group-ID mode bit of the new process file is set, the effective group ID of the new process is set to the group ID of the new process file.  The real user ID and real group ID of the new process remain the same as those of the calling process. 

The shared memory segments attached to the calling process are not attached to the new process [see shmop(2)].

Profiling is disabled for the new process; see profil(2).

The new process also inherits the following attributes from the calling process:

nice value [see nice(2)]

process ID

parent process ID

process group ID

semadj values [see semop(2)]

tty group ID [see exit(2) and signal(2)]

trace flag [see ptrace(2) request 0]

time left until an alarm clock signal [see alarm(2)]

current working directory

root directory

file mode creation mask [see umask(2)]

file size limit [see ulimit(2)]

utime, stime, cutime, and cstime [see times(2)]

file-locks [see fcntl(2) and lockf(3C)]

exec will fail and return to the calling process if one or more of the following are true:

­[ENOENT] One or more components of the new process path name of the file do not exist. 

­[ENOTDIR] A component of the new process path of the file prefix is not a directory. 

­[EACCES] Search permission is denied for a directory listed in the new process file’s path prefix. 

­[EACCES] The new process file is not an ordinary file. 

­[EACCES] The new process file mode denies execution permission. 

­[ENOEXEC] The exec is not an execlp or execvp, and the new process file has the appropriate access permission but an invalid magic number in its header.

­[ENOEXEC] A multi-threaded process may not exec.

­[ETXTBSY] The new process file is a pure procedure (shared text) file that is currently open for writing by some process. 

­[ENOMEM] The new process requires more memory than is allowed by the system-imposed maximum MAXMEM. 

­[E2BIG] The number of bytes in the new process’s argument list is greater than the system-imposed limit of NCARGS bytes. 

­[EFAULT] path, argv, or envp point to an illegal address. 

­[EAGAIN] Not enough memory. 

­[ELIBACC] Required shared library does not have execute permission. 

­[ELIBEXEC] Trying to exec(2) a shared library directly. 

­[EINTR] A signal was caught during the exec system call. 

SEE ALSO

a.out(4), alarm(2), environ(5), exit(2), fcntl(2), fork(2), lockf(3C), nice(2), ptrace(2), semop(2), sh(1), signal(2), sigset(2), spawn(2), thread(2), times(2), ulimit(2), umask(2)

DIAGNOSTICS

If exec returns to the calling process an error has occurred; the return value will be −1 and errno will be set to indicate the error. 

September 02, 1992