名稱

chmod, fchmod - 更改文件的權限

內容簡介

#include

#include

int chmod(const char \*path, mode\_t mode); int fchmod(int fildes, mode\_t mode); 

描述

給定的文件路徑或引用fildes的的模式改變。

所指定的「或」以下模式：

標籤

描述

S_ISUID

04000 set user ID on execution

S_ISGID

02000 set group ID on execution

S_ISVTX

01000 sticky bit

S_IRUSR

00400 read by owner

S_IWUSR

00200 write by owner

S_IXUSR

00100 execute/search by owner

S_IRGRP

00040 read by group

S_IWGRP

00020 write by group

S_IXGRP

00010 execute/search by group

S_IROTH

00004 read by others

S_IWOTH

00002 write by others

S_IXOTH

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 CAP_FOWNER capability).

If the calling process is not privileged (Linux: does not have the CAP_FSETIDcapability), 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.

返回值

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

錯誤

根據文件系統上的，其他錯誤，也可以返回，chmod() 更普遍的錯誤列舉如下：

Error Code

描述

EACCES

Search permission is denied on a component of the path prefix. (See also path_resolution(2).)

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 theCAP_FOWNER capability).

EROFS

The named file resides on a read-only file system.

The general errors for fchmod() are listed below:

EBADF

The file descriptor fildes is not valid.

EIO

See above.

EPERM

See above.

EROFS

See above.

遵循於

4.4BSD, SVr4, POSIX.1-2001.

另請參閱

• chown (2)

• execve (2)

• fchmodat (2)

• open (2)

• path_resolution (2)

• stat (2)