chmod(S) 6 January 1993 chmod(S) Name chmod - change mode of file Syntax cc . . . -lc int chmod (path, mode) char *path; int 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 accord- ing 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 be super-user to change the mode of a file. If the effective user ID of the process is not super-user and the file is not a directory, mode bit 01000 (save text image on execution) is cleared. If the effective user ID of the process is not super-user and the effec- tive 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 410 executable file has the sticky bit (mode bit 01000) set, the op- erating 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 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. 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(S)): + the user owns the file + the user owns the directory + the file is writable to the user + the user is the super-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 effect future calls to open(S), creat(S), read(S), and write(S) 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 pre- fix. [EPERM] The effective user ID does not match the owner of the file and the effective user ID is not super-user. [EROFS] The named file resides on a read-only file system. [EFAULT] path points outside the allocated address space of the pro- cess. [EINTR] A signal was caught during the chmod system call. [ENOLINK] path points to a remote machine and the link to that machine is no longer active. [EMULTIHOP] Components of path require hopping to multiple remote ma- chines. 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. See also chown(S), chmod(C), creat(S), fcntl(S), mknod(S), open(S), read(S), write(S) Standards conformance chmod conforms with: AT&T SVID Issue 2; X/Open Portability Guide, Issue 3, 1989; Intel386 Binary Compatibility Specification, Edition 2 (iBCSe2); IEEE POSIX Std 1003.1-1990 System Application Program Interface (API) [C Language] (ISO/IEC 9945-1); and NIST FIPS 151-1.