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CHMOD
Section: Linux Programmer's Manual (2)
Updated: 10 December 1997
Index NAME
chmod, fchmod - change permissions of a 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
The mode of the file given by
pathor referenced by
fildesis changed.
Modes are specified byor'ingthe following:
- S_ISUID
- 04000 set user ID on execution
- S_ISGID
- 02000 set group ID on execution
- S_ISVTX
- 01000 sticky bit
- S_IRUSR (S_IREAD)
- 00400 read by owner
- S_IWUSR (S_IWRITE)
- 00200 write by owner
- S_IXUSR (S_IEXEC)
- 00100 execute/search by owner
- S_IRGRP
- 00040 read by group
- S_IWGRP
- 00020 write by group
- S_IXGRP
- 00010 execute/search by group
- S_IROTH
- 00004 read by others
- S_IWOTH
- 00002 write by others
- S_IXOTH
- 00001 execute/search by others
The effective UID of the process must be zero or must match the owner ofthe file.
If the effective UID of the process is not zero and the group of the filedoes not match the effective group ID of the process or one of itssupplementary group IDs, the S_ISGID bit will be turned off,but this will not cause an error to be returned.
Depending on the file system, set user ID and set group ID execution bitsmay be turned off if a file is written. On some file systems, only thesuper-user can set the sticky bit, which may have a special meaning (e.g.,for directories, a file can only be deleted by the owner or the super-user).
On NFS file systems, restricting the permissions will immediately influencealready open files, because the access control is done on the server, butopen files are maintained by the client. Widening the permissions may bedelayed for other clients if attribute caching is enabled on them.
RETURN VALUE
On success, zero is returned. On error, -1 is returned, and
errnois set appropriately.
ERRORS
Depending on the file system, other errors can be returned. The moregeneral errors for
chmodare listed below:
- EPERM
- The effective UID does not match the owner of the file, and is not zero.
- EROFS
- The named file resides on a read-only file system.
- EFAULT
- pathpoints outside your accessible address space.
- ENAMETOOLONG
- pathis too long.
- ENOENT
- The file does not exist.
- ENOMEM
- Insufficient kernel memory was available.
- ENOTDIR
- A component of the path prefix is not a directory.
- EACCES
- Search permission is denied on a component of the path prefix.
- ELOOP
- Too many symbolic links were encountered in resolvingpath.
- EIO
- An I/O error occurred.
The general errors forfchmodare listed below:
- EBADF
- The file descriptorfildesis not valid.
- EROFS
- See above.
- EPERM
- See above.
- EIO
- See above.
CONFORMING TO
The
chmodcall conforms to SVr4, SVID, POSIX, X/OPEN, 4.4BSD.SVr4 documents EINTR, ENOLINK and EMULTIHOP returns, but noENOMEM. POSIX.1 does not document EFAULT, ENOMEM, ELOOP or EIO errorconditions, or the macros
S_IREAD,
S_IWRITE and
S_IEXEC.
The fchmodcall conforms to 4.4BSD and SVr4.SVr4 documents additional EINTR and ENOLINK error conditions.POSIX requires thefchmodfunction if at least one of_POSIX_MAPPED_FILESand_POSIX_SHARED_MEMORY_OBJECTSis defined, and documents additional ENOSYS and EINVAL errorconditions, but does not document EIO.
POSIX and X/OPEN do not document the sticky bit.
SEE ALSO
open(2),
chown(2),
stat(2)
Index
- NAME
- SYNOPSIS
- DESCRIPTION
- RETURN VALUE
- ERRORS
- CONFORMING TO
- SEE ALSO
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