chmod(2P) INTERACTIVE UNIX System (POSIX) chmod(2P)
NAME
chmod - change mode of file
SYNOPSIS
#include <sys/types.h>
#include <sys/stat.h>
int chmod (path, mode)
char *path;
mode_t mode;
DESCRIPTION
The path argument points to a path name naming a file. The
chmod system call sets the access permission portion of the
named file's mode according to the bit pattern contained in
mode.
Access permission bits are interpreted as follows:
04000
Set user ID on execution.
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.
01000
Save text image after execution.
00400
Read by owner.
00200
Write by owner.
00100
Execute (search if a directory) by owner.
00070
Read, write, execute (search) by group.
00007
Read, write, execute (search) by others.
The effective user ID of the process must match the owner of
the file or the calling process must have the appropriate
privileges to change the mode of a file.
If the calling process does not have the appropriate
privileges and the file is not a directory, mode bit 01000
(save text image on execution) is cleared.
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chmod(2P) INTERACTIVE UNIX System (POSIX) chmod(2P)
If the calling process does not have the appropriate
privileges and the effective group ID of the process does
not match the group ID of the file or one of the supplemen-
tary group IDs, mode bit 02000 (set group ID on execution)
is cleared.
If a 410 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 413 executable file has the sticky bit set, the operat-
ing 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.
The file creation system calls will use the set group ID bit
of the file mode of the directory containing the new file to
determine the group ID of this new file. If this bit is not
set, the group ID of this new file will be assigned its
parent ID of the process. Otherwise, it will be assigned
the group ID of the containing directory. When creating a
new directory, the value of the set group ID bit of the file
mode of the new directory will be inherited from the direc-
tory containing the new directory.
Overall, if a directory is writable and has the sticky bit
set, files within that directory can only be removed if one
or more of the following is true (see unlink(2)):
The user owns the file.
The user owns the directory.
The file is writable to the user.
The user is the superuser.
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 effect future calls to open(2P), creat(2),
read(2P), and write(2P) on this file.
chmod will fail and the file mode will be unchanged if one
or more of the following is true:
[ENOTDIR] A component of the path prefix is not a
directory.
[ENOENT] The named file does not exist.
[EACCES] Search permission is denied on a component of
the path prefix.
[EPERM] The effective user ID does not match the
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chmod(2P) INTERACTIVE UNIX System (POSIX) chmod(2P)
owner of the file and the effective user ID
is not superuser.
[EROFS] The named file resides on a read-only file
system.
[EFAULT] The path variable points outside the allo-
cated address space of the process.
[EINTR] A signal was caught during the chmod system
call.
[ENOLINK] The path variable points to a remote machine
and the link to that machine is no longer
active.
[EMULTIHOP] Components of path require hopping to multi-
ple remote machines.
[ENAMETOOLONG] The length of the path argument exceeds
{PATH_MAX}, or a path name component is
longer than {NAME_MAX} while
{_POSIX_NO_TRUNC} is in effect.
SEE ALSO
chown(2P), creat(2), fcntl(2), mknod(2), open(2P), read(2P),
write(2P.
chmod(1) in the INTERACTIVE UNIX System User's/System
Administrator's Reference Manual.
DIAGNOSTICS
Upon successful completion, a value of 0 is returned. Oth-
erwise, a value of -1 is returned, and errno is set to indi-
cate the error.
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