chmod(2)
Name
chmod, fchmod − change mode of file
Syntax
#include <sys/types.h>
#include <sys/stat.h>
chmod(path, mode)
char *path;
mode_t mode;
fchmod(fd, mode)
int fd;
mode_t mode;
Description
The file whose name is provided by path or referenced by the descriptor fd has its mode changed to mode. Modes are constructed by ORing combinations of the following:
S_ISUID− 04000 set user ID on execution
S_ISGID− 02000 set group ID on execution
S_ISVTX− 01000 save text image after execution
S_IRUSR− 00400 read by owner
S_IWUSR− 00200 write by owner
S_IXUSR− 00100 execute (search on directory) by owner
S_IRWXG− 00070 read, write, execute (search) by group
S_IRWXO− 00007 read, write, execute (search) by others
If an executable file is set up for sharing (the default), the mode S_ISVTX prevents the system from abandoning the swap-space image of the program-text portion of the file when its last user terminates. The ability to set this bit is restricted to the superuser.
If the mode S_ISVTX (sticky bit) is set on a directory, an unprivileged user cannot delete or the rename files of other users in that directory. For more information on the sticky bit, see sticky(.).
Only the owner of a file or the superuser can change the mode.
Writing a file or changing the owner of a file clears the set-user-id and set-group-id bits of that file. Turning off these bits when a file is written or its owner changed protects the file from remaining set-user-id or set-group-id after being modified. If a file, specifically a program, remained set-user-id or set-group-id after being modified, that file could allow unauthorized access to other files or accounts.
Environment
System Five
ELOOP is a possible error condition.
Return Values
Upon successful completion, a value of 0 is returned. Otherwise, a value of −1 is returned, and errno is set to indicate the error.
Diagnostics
The chmod system call fails and the file mode remains unchanged under the following conditions:
[EACCES] Search permission is denied on a component of the path prefix.
[EFAULT] The path argument points outside the process’s allocated address space.
[EIO] An I/O error occurred while reading from or writing to the file system.
[ELOOP] Too many symbolic links were encountered in translating the pathname.
[ENAMETOOLONG]
A pathname component exceeds 255 characters, or an entire pathname exceeds 1023 characters.
[ENOENT] The named file does not exist.
[ENOTDIR] A component of the path prefix is not a directory.
[EPERM] The effective user ID does not match the owner of the file and the effective user ID is not the superuser.
[EROFS] The named file resides on a read-only file system.
[ESTALE] The file handle given in the argument is invalid. Either the file referred to by that file handle no longer exists or it has been revoked.
The fchmod system call fails under the following conditions:
[EBADF] The descriptor is not valid.
[EINVAL] The fd refers to a socket, not to a file.
[EIO] An I/O error occurred while reading from or writing to the file system.
[EROFS] The file resides on a read-only file system.
[ETIMEDOUT] A connect request or remote file operation failed because the connected party did not respond after a period of time determined by the communications protocol.