NAME
chmod, fchmod - change permissions of a file SYNOPSIS
#include
int chmod(const char *path, modet mode); int fchmod(int fd, modet mode); Feature Test Macro Requirements for glibc (see featuretestmacros(7)): fchmod(): BSDSOURCE || XOPENSOURCE >= 500 || XOPENSOURCE && XOPENSOURCEEXTENDED || /* Since glibc 2.12: */ POSIXCSOURCE >= 200809L DESCRIPTION These system calls change the permissions of a file. They differ only in how the file is specified: * chmod() changes the permissions of the file specified whose pathname is given in path, which is dereferenced if it is a symbolic link. * fchmod() changes the permissions of the file referred to by the open file descriptor fd. The new file permissions are specified in mode, which is a bit mask created by ORing together zero or more of the following: SISUID (04000) set-user-ID (set process effective user ID on execve(2))
SISGID (02000) set-group-ID (set process effective group ID on execve(2); mandatory locking, as described in fcntl(2); take a new file's group from parent direc‐ tory, as described in chown(2) and mkdir(2)) SISVTX (01000) sticky bit (restricted deletion flag, as described in unlink(2)) SIRUSR (00400) read by owner SIWUSR (00200) write by owner SIXUSR (00100) execute/search by owner ("search" applies for direc‐ tories, and means that entries within the directory can be accessed) SIRGRP (00040) read by group SIWGRP (00020) write by group SIXGRP (00010) execute/search by group SIROTH (00004) read by others SIWOTH (00002) write by others SIXOTH (00001) execute/search by others The effective UID of the calling process must match the owner of the file, or the process must be privileged (Linux: it must have the CAPFOWNER capability). If the calling process is not privileged (Linux: does not have the CAPFSETID capability), and the group of the file does not match the effective group ID of the process or one of its supplementary group IDs, the SISGID bit will be turned off, but this will not cause an error to be returned.
As a security measure, depending on the file system, the set-user-ID
and set-group-ID execution bits may be turned off if a file is written. (On Linux this occurs if the writing process does not have the CAPFSETID capability.) On some file systems, only the superuser can set the sticky bit, which may have a special meaning. For the sticky
bit, and for set-user-ID and set-group-ID bits on directories, see stat(2). On NFS file systems, restricting the permissions will immediately influence already open files, because the access control is done on the server, but open files are maintained by the client. Widening the per‐ missions may be delayed for other clients if attribute caching is enabled on them. RETURN VALUE
On success, zero is returned. On error, -1 is returned, and errno is set appropriately. ERRORS Depending on the file system, other errors can be returned. The more general errors for chmod() are listed below: EACCES Search permission is denied on a component of the path prefix. (See also pathresolution(7).) EFAULT path points outside your accessible address space. EIO An I/O error occurred. ELOOP Too many symbolic links were encountered in resolving path. ENAMETOOLONG path is 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. EPERM The effective UID does not match the owner of the file, and the process is not privileged (Linux: it does not have the CAPFOWNER capability).
EROFS The named file resides on a read-only file system. The general errors for fchmod() are listed below: EBADF The file descriptor fd is not valid. EIO See above. EPERM See above. EROFS See above. CONFORMING TO
4.4BSD, SVr4, POSIX.1-2001. SEE ALSO chown(2), execve(2), fchmodat(2), open(2), stat(2), pathresolution(7) COLOPHON
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Linux 2010-09-26 CHMOD(2)