NAME

chmod – change access permission mode of file

SYNOPSIS

#include <sys/types.h>
#include <sys/stat.h>

int chmod(const char *path , mode_t mode );

DESCRIPTION

chmod() sets the access permission portion of the mode of the file whose name is given by path to the bit pattern contained in mode . Modes are constructed by ORing the access permission bits.

The effective user ID of the thread must match the owner of the file or the thread must have the appropriate privilege to change the mode of a file.

If the thread is not privileged and the file is not a directory, mode bit 01000 (save text image on execution) is cleared.

If a directory is writable and has S_ISVTX (the sticky bit) set, files within that directory can be removed or renamed only if one or more of the following is true (see unlink (2) and rename (2)):

(bu the user owns the file (bu the user owns the directory (bu the file is writable by the user (bu the user is a privileged user

If a directory has the set group ID bit set, a given file created within that directory will have the same group ID as the directory, if that group ID is part of the group ID set of the thread that created the file. Otherwise, the newly created file’s group ID will be set to the effective group ID of the creating thread.

If the mode bit 02000 (set group IDon 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 affect future calls to open (2), creat (2), read (2), and write (2) on this file.

Upon successful completion, chmod() marks for update the st_ctime field of the file.

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

This function is a member of Unison’s IOLIB family of functions. IOLIB is implemented as a message passing and generalized interface layer. Each Unison I/O server is responsible for its own error reporting.

For an exact list of error codes returned by a particular server, refer to that server’s documentation in the Unison Programmer’s Guide for each specific platform.

Servers may implement these errors codes in response to this function.

chmod() will fail and the file mode will be unchanged if one or more of the following are true:

EACCES

Search permission is denied on a component of the path prefix of

EFAULT

path points to an illegal address.

EIO

An I/O error occurred while reading from or writing to the file system.

EMULTIHOP

Components of path require hopping to multiple remote machines and file system type does not allow it.

ENAMETOOLONG

The length of the path argument exceeds { PATH_MAX }, or the length of a path component exceeds { NAME_MAX } while { _POSIX_NO_TRUNC } is in effect.

ENOENT

Either a component of the path prefix, or the file referred to by path does not exist or is a null pathname.

ENOLINK

fildes points to a remote machine and the link to that machine is no longer active.

ENOTDIR

A component of the prefix of path is not a directory.

EPERM

The effective user ID does not match the owner of the file and is not super-user.

EROFS

The file referred to by path resides on a read-only file system.

SEE ALSO

mkdir(), open(), stat()