chmod(2) chmod(2)
NAME
chmod, fchmod - change mode of file
SYNOPSIS
#include <sys/types.h>
#include <sys/stat.h>
int chmod(const char *path, mode_t mode);
int fchmod(int fildes, mode_t mode);
DESCRIPTION
chmod and fchmod set the access permission portion of the mode
of the file whose name is given by path or referenced by the
descriptor fildes to the bit pattern contained in mode. If
path or fildes are symbolic links, the access permissions of
the target of the symbolic links are set. Access permission
bits are interpreted as follows:
S_ISUID 04000 Set user ID on execution.
S_ISGID 020#0 Set group ID on execution if # is 7, 5, 3, or 1
Enable mandatory file/record locking if # is 6, 4, 2, or 0
S_ISVTX 01000 Save text image after execution.
S_IRWXU 00700 Read, write, execute by owner.
S_IRUSR 00400 Read by owner.
S_IWUSR 00200 Write by owner.
S_IXUSR 00100 Execute (search if a directory) by owner.
S_IRWXG 00070 Read, write, execute by group.
S_IRGRP 00040 Read by group.
S_IWGRP 00020 Write by group.
S_IXGRP 00010 Execute by group.
S_IRWXO 00007 Read, write, execute (search) by others.
S_IROTH 00004 Read by others.
S_IWOTH 00002 Write by others
S_IXOTH 00001 Execute by others.
Modes are constructed by an OR of the access permission bits.
The effective user ID of the process must match the owner of
the file or the process must have the appropriate privilege to
change the mode of a file.
If the process does not have appropriate privilege and the
file is not a directory, mode bit 01000 (save text image on
execution) is cleared.
Copyright 1994 Novell, Inc. Page 1
chmod(2) chmod(2)
If the effective group ID of the process does not match the
group ID of the file, and the process does not have
appropriate privilege mode bit 02000 (set group ID on
execution) is cleared.
If a 0410 executable file has the sticky bit (mode bit 01000)
set, the operating system will not delete the program text
from the swap area when the last user process terminates. If
a 0413 or ELF executable file has the sticky bit set, the
operating system will not delete the program text from memory
when the last user process terminates. In either case, if the
sticky bit is set the text will already be available (either
in a swap area or in memory) when the next user of the file
executes it, thus making execution faster.
If a directory is writable and the sticky bit, S_ISVTX, is set
on the directory, a process may remove or rename files within
that directory only if one or more of the following is true:
the effective user ID of the process is the same as that
of the owner ID of the file
the effective user ID of the process is the same as that
of the owner ID of the directory
the process has write permission for the file.
the process has appropriate privileges
If the mode bit 02000 (set group ID on execution) is set and
the mode bit 00010 (execute or search by group) is not set,
mandatory file/record locking will exist on a regular file.
This may affect future calls to open(2), creat(2), read(2),
and write(2) on this file.
The following environment variables affect the execution of
chmod
LC_MESSAGES
Determines the locale to be used for diagnostic
messages. If available, these messages will be
retrieved from the message data base, uxcore.abi.
LC_ALL If a non-empty string, this overrides the values of all
the other internationalization variables.
Copyright 1994 Novell, Inc. Page 2
chmod(2) chmod(2)
LANG The default value for internationalization variables
that are unset or null.
Return Values
On success, chmod and fchmod return 0 and mark for update the
st_ctime field of the file. On failure, chmod and fchmod
return -1, set errno to identify the error, and the file mode
is unchanged.
Errors
In the following conditions, chmod fails and sets errno to:
EACCES Search permission is denied on a component of the path
prefix of path.
EACCES Write permission on the named file is denied.
EFAULT path points outside the allocated address space of the
process.
EINTR A signal was caught during execution of the system call.
EIO An I/O error occurred while reading from or writing to
the file system.
ELOOP Too many symbolic links were encountered in translating
path.
EMULTIHOP
Components of path require hopping to multiple remote
machines and file system type does not allow it.
ENAMETOOLONG
The length of the path argument exceeds {PATH_MAX}, or
the length of a path component exceeds {NAME_MAX} while
_POSIX_NO_TRUNC is in effect.
ENOTDIR
A component of the prefix of path is not a directory.
ENOENT Either a component of the path prefix, or the file
referred to by path does not exist or is a null
pathname.
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chmod(2) chmod(2)
ENOLINK
fildes points to a remote machine and the link to that
machine is no longer active.
EPERM The effective user ID does not match the owner of the
file and the process does not have appropriate
privilege (P_OWNER).
EROFS The file referred to by path resides on a read-only file
system.
In the following conditions, fchmod fails and sets errno to:
EBADF fildes is not an open file descriptor
EIO An I/O error occurred while reading from or writing to
the file system.
EINTR A signal was caught during execution of the fchmod
system call.
ENOLINK
path points to a remote machine and the link to that
machine is no longer active.
EPERM The effective user ID does not match the owner of the
file and the process does not have appropriate
privilege (P_OWNER).
EROFS The file referred to by fildes resides on a read-only
file system.
REFERENCES
access(2), chmod(1) chown(2), creat(2), exec(2), fcntl(2),
mkfifo(3C), mknod(2), open(2), read(2), stat(2), stat(5),
write(2)
Copyright 1994 Novell, Inc. Page 4