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, 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 execution) 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 terminates. If a 0413 or ELF
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chmod(2) chmod(2)
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 component 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 component
exceeds {NAMEMAX} while POSIXNOTRUNC is in
effect.
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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 Programmer's Guide:
System Services and Application Packaging Tools.
DIAGNOSTICS
Upon successful completion, a value of 0 is returned. Otherwise, a
value of -1 is returned and errno is set to indicate the error.
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