chmod(2) SYSTEM CALLS chmod(2)
NAME
chmod, fchmod - change mode of file
SYNOPSIS
#include <sys/types.h>
#include <sys/stat.h>
int chmod(const char *path, modet mode);
int fchmod(int fildes, modet 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. Access permission bits are interpreted as follows:
SISUID 04000 Set user ID on execution.
SISGID 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
SISVTX 01000 Save text image after execution.
SIRWXU 00700 Read, write, execute by owner.
SIRUSR 00400 Read by owner.
SIWUSR 00200 Write by owner.
SIXUSR 00100 Execute (search if a directory) by owner.
SIRWXG 00070 Read, write, execute by group.
SIRGRP 00040 Read by group.
SIWGRP 00020 Write by group.
SIXGRP 00010 Execute by group.
SIRWXO 00007 Read, write, execute (search) by others.
SIROTH 00004 Read by others.
SIWOTH 00002 Write by others
SIXOTH 00001 Execute by others.
Modes are constructed by OR'ing 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 is not a privileged process and the file is
not a directory, mode bit 01000 (save text image on execu-
tion) is cleared.
If neither the process nor a member of the supplementary
group list is privileged, and the effective group ID of the
process does not match the group ID of the file, 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
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chmod(2) SYSTEM CALLS chmod(2)
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 has the sticky bit set, files
within that directory can be removed or renamed only if one
or more of the following is true [see unlink(2) and
rename(2)]:
the user owns the file
the user owns the directory
the file is writable by the user
the user is a privileged user
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.
Upon successful completion, chmod and fchmod mark for update
the stctime field of the file.
chmod will fail and the file mode will be unchanged if one
or more of the following are true:
EACCES Search permission is denied on a com-
ponent of the path prefix of path.
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
{PATHMAX}, or the length of a path
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chmod(2) SYSTEM CALLS chmod(2)
component exceeds {NAMEMAX} while
POSIXNOTRUNC 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.
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.
EROFS The file referred to by path resides on
a read-only file system.
fchmod will fail and the file mode will be unchanged if:
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.
EROFS The file referred to by fildes resides
on a read-only file system.
SEE ALSO
chown(2), creat(2), fcntl(2), mknod(2), open(2), read(2),
stat(2), write(2), mkfifo(3C), stat(5).
chmod(1) in the User's Reference Manual.
The "File and Record Locking" chapter in the Application
Programmer's Guide.
DIAGNOSTICS
Upon successful completion, a value of 0 is returned. Oth-
erwise, a value of -1 is returned and errno is set to
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chmod(2) SYSTEM CALLS chmod(2)
indicate the error.
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