CHMOD(2) System Calls Manual CHMOD(2)NAME
chmod - change mode of file
SYNOPSIS
chmod(name, mode)
char *name;
DESCRIPTION
The file whose name is given as the null-terminated string pointed to by name has its mode changed to mode. Modes are constructed by ORing
together some combination of the following:
04000 set user ID on execution
02000 set group ID on execution
01000 save text image after execution
00400 read by owner
00200 write by owner
00100 execute (search on directory) by owner
00070 read, write, execute (search) by group
00007 read, write, execute (search) by others
If an executable file is set up for sharing (-n or -i option of ld(1)) then mode 1000 prevents the system from abandoning the swap-space
image of the program-text portion of the file when its last user terminates. Thus when the next user of the file executes it, the text
need not be read from the file system but can simply be swapped in, saving time. Ability to set this bit is restricted to the super-user
since swap space is consumed by the images; it is only worth while for heavily used commands.
Only the owner of a file (or the super-user) may change the mode. Only the super-user can set the 1000 mode.
SEE ALSO chmod(1)DIAGNOSTIC
Zero is returned if the mode is changed; -1 is returned if name cannot be found or if current user is neither the owner of the file nor the
super-user.
ASSEMBLER
(chmod = 15.)
sys chmod; name; mode
CHMOD(2)
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CHMOD(2) System Calls Manual CHMOD(2)NAME
chmod - change mode of file
SYNOPSIS
chmod(path, mode)
char *path;
int mode;
fchmod(fd, mode)
int fd, mode;
DESCRIPTION
The file whose name is given by path or referenced by the descriptor fd has its mode changed to mode. Modes are constructed by or'ing
together some combination of the following, defined in <sys/inode.h>:
ISUID 04000 set user ID on execution
ISGID 02000 set group ID on execution
ISVTX 01000 `sticky bit' (see below)
IREAD 00400 read by owner
IWRITE 00200 write by owner
IEXEC 00100 execute (search on directory) by owner
00070 read, write, execute (search) by group
00007 read, write, execute (search) by others
If an executable file is set up for sharing (this is the default) then mode ISVTX (the `sticky bit') prevents the system from abandoning
the swap-space image of the program-text portion of the file when its last user terminates. Ability to set this bit on executable files is
restricted to the super-user.
If mode ISVTX (the `sticky bit') is set on a directory, an unprivileged user may not delete or rename files of other users in that direc-
tory. For more details of the properties of the sticky bit, see sticky(8).
Only the owner of a file (or the super-user) may change the mode.
Writing or changing the owner of a file turns off the set-user-id and set-group-id bits unless the user is the super-user. This makes the
system somewhat more secure by protecting set-user-id (set-group-id) files from remaining set-user-id (set-group-id) if they are modified,
at the expense of a degree of compatibility.
RETURN VALUE
Upon successful completion, a value of 0 is returned. Otherwise, a value of -1 is returned and errno is set to indicate the error.
ERRORS
Chmod will fail and the file mode will be unchanged if:
[ENOTDIR] A component of the path prefix is not a directory.
[EINVAL] The pathname contains a character with the high-order bit set.
[ENAMETOOLONG] A component of a pathname exceeded 255 characters, or an entire path name exceeded 1023 characters.
[ENOENT] The named file does not exist.
[EACCES] Search permission is denied for a component of the path prefix.
[ELOOP] Too many symbolic links were encountered in translating the pathname.
[EPERM] The effective user ID does not match the owner of the file and the effective user ID is not the super-user.
[EROFS] The named file resides on a read-only file system.
[EFAULT] Path points outside the process's allocated address space.
[EIO] An I/O error occurred while reading from or writing to the file system.
Fchmod will fail if:
[EBADF] The descriptor is not valid.
[EINVAL] Fd refers to a socket, not to a file.
[EROFS] The file resides on a read-only file system.
[EIO] An I/O error occurred while reading from or writing to the file system.
SEE ALSO chmod(1), open(2), chown(2), stat(2), sticky(8)4th Berkeley Distribution May 13, 1986 CHMOD(2)