chmod

chmod, fchmod - change permissions of a file

#include <sys/types.h>
#include <sys/stat.h> I int chmod(const char * path , mode_t mode );
I int fchmod(int fildes , mode_t mode );

The mode of the file given by path or referenced by fildes is changed. Modes are specified by R or'ing the following:

S_ISUID

S_ISGID

S_ISVTX

S_IRUSR

S_IWUSR

S_IXUSR

S_IRGRP

S_IWGRP

S_IXGRP

S_IROTH

S_IWOTH

S_IXOTH

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 CAP_FOWNER capability). If the calling process is not privileged (Linux: does not have the CAP_FSETID 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 S_ISGID 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 CAP_FSETID 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 permissions may be delayed for other clients if attribute caching is enabled on them.

On success, zero is returned. On error, -1 is returned, and errno is set appropriately.

Depending on the file system, other errors can be returned. The more general errors for R chmod () are listed below:

EACCES

EFAULT

EIO

ELOOP

ENAMETOOLONG

ENOENT

ENOMEM

ENOTDIR

EPERM

EROFS

The general errors for R fchmod () are listed below:

EBADF

EIO

EPERM

EROFS

4.4BSD, SVr4, POSIX.1-2001.

chown(2), execve(2), fchmodat(2), open(2), stat(2), path_resolution(7)