chmod()

NAME

chmod(), fchmod() - change mode of file

SYNOPSIS 

#include <sys/stat.h>


int chmod (const char *path, mode_t mode)
int fchmod (int fildes, mode_t mode)

DESCRIPTION

The function chmod(2) sets the file permission bits of the file specified by the pathname path to mode. The fchmod(2) does the same, except that the file is specified by the file descriptor filedes.

Chmod(2) and fchmod(2) verify that the process owner (user) owns the file specified by path. A mode is created from OR'd permission bit masks defined in <sys/stat.h>:

Symbol Value Meaning
S_IRWXU 0000700 RWX mask for owner
S_IRUSR 0000400 R for owner
S_IWUSR 0000200 W for owner
S_IXUSR 0000100 X for owner
S_IRWXG 0000070 RWX mask for group
S_IRGRP 0000040 R for group
S_IWGRP 0000020 W for group
S_IXGRP 0000010 X for group
S_IRWXO 0000007 RWX mask for other
S_IROTH 0000004 R for other
S_IWOTH 0000002 W for other
S_IXOTH 0000001 X for other
S_ISUID 0004000 set user ID on execution; see NOTES later in this topic
S_ISGID 0002000 set group ID on execution; see NOTES later in this topic

Calling the chmod(2) function on a file with open file descriptors has no effect on the open file descriptors.

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.

ERRORS

The chmod(2) function will fail and the file mode will be unchanged if:

[EACCES]
Search permission is denied for a component of the path prefix.
[EFAULT]
Path points outside the process's allocated address space.
[EINVAL]
The pathname contains a character with the high-order bit set, or the operation is not valid on this type of file (such as a pipe or a socket).
[EIO]
An I/O error occurred while reading from or writing to the file system.
[ENAMETOOLONG]

A component of a pathname exceeded {NAME_MAX} characters, or an entire pathname exceeded {PATH_MAX} characters.
[ENOENT]
The named file does not exist.
[ENOTDIR]
A component of the path prefix is not a directory.
[ELOOP]
Too many symbolic links were encountered in translating the pathname.
[EOPNOTSUPP ]
The mode argument specified permissions other than S_IRWXU, S_IRWXG, and S_IRWXO for a file on a file system (such as FAT) that doesn't support the additional permissions.
[EPERM]
The effective user ID does not match the owner of the file.
[EROFS]
The named file resides on a read-only file system.

The fchmod(2) function can fail for the following reasons:

[EBADF]
The fildes is not an open file descriptor.
[EINTR]
The call was interrupted by a signal.
[EINVAL]
The mode was invalid, or the operation is not valid on this type of file (such as a pipe or a socket).
[EPERM]
The named file resides on a read-only file system.
[EROFS]
The file is on a read-only file system.

NOTES

When you use chmod(2) or fchmod(2) to make a file writeable, the function will unset the Win32 Read-Only attribute, if it is set on the file. (If the Read-Only attribute is set, the stat(2) function will report that the file is not writeable, regardless of the permissions on the ACLs associated with the file.)

By default, Interix does not execute files with the set-user-ID (setuid) or set-group-ID (setgid) mode bit set for security reasons. If an attempt is made to execute such a file, the ENOSETUID error is returned. For more information and and instructions for enabling execution of files with these mode bits set, see The superuser account and appropriate privileges in Windows Services for UNIX Help.

SEE ALSO

chmod(1)

open(2)

chown(2)

stat(2)

privileges(5)