chmod(2)

NAME

chmod, fchmod − change mode of file

SYNOPSIS

#include <sys/types.h>
#include <sys/stat.h>
int chmod (path, mode)
char ∗path;
mode_t mode;

SYNOPSIS (4.2BSD)

#include <sys/types.h>
#include <sys/stat.h>
int fchmod (fd, mode)
int fd;
mode_t mode;

DESCRIPTION

chmod sets the access permission portion of a file’s mode according to the bit pattern contained in mode. Path points to the file’s path name. Using fchmod, the file may be specified by descriptor fd.

Access permission bits are interpreted as follows:

S_ISUID Set user ID on execution.

S_ISGID Set group ID on execution.

S_ISVTX Save text image after execution.

S_IRUSR Read by owner.

S_IWUSR Write by owner.

S_IXUSR Execute (search if a directory) by owner.

S_IRGRP Read by group.

S_IWGRP Write by group.

S_IXGRP Execute (search) by group.

S_IROTH Read by others (i.e., by anyone else).

S_IWOTH Write by others.

S_IXOTH Execute (search) by others.

S_ENFMT Record locking enforced.

The effective user ID of the process must match the owner of the file or be super-user to change the mode of a file.

If the effective user ID of the process is not super-user, the effective label of the calling process (current security label) must match the label of the file identically. (B1 only)

If the effective user ID of the process is not super-user or the user does not have the ACC_SET_VEC effective access vector (if configured), mode bit S_ISVTX (save text image on execution) is cleared.

If the effective user ID of the process is not super-user and the effective group ID of the process does not match the group ID of the file, mode bit S_ISGID (set group ID on execution) is cleared.

If an executable file is prepared for sharing then mode bit S_ISVTX prevents the system from abandoning the swap-space image of the program-text portion of the file when its last user terminates. Thus, when the next user of the file executes it, the text need not be read from the file system but can simply be swapped in, saving time.

For ordinary files, if the mode bit S_ENFMT (record locking enforced) is set and the mode bit S_IXGRP (execute or search by group) is not set, enforced record locking is enabled. This will affect future calls to open(2), creat(2), read(2), and write(2) routines on this file. If these conditions are not met, all locks on the file will be advisory (see fcntl(2)).

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.

[EFAULT] Path points outside the allocated address space of the process.

[ENAMETOOLONG] The path argument exceeds {PATH_MAX} in length, or a pathname component is longer than {NAME_MAX} (see pathconf(2)).

[ENOTDIR] A component of the path prefix is not a directory.

[ENOENT] The named file does not exist, or the path argument points to an empty string.

[EPERM] The effective user ID does not match the owner of the file and the effective user ID is not super-user, or the current effective security label does not match the classification of the file and the effective user ID is not super-user. (B1 only)

[EROFS] The named file resides on a read-only file system.

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

[EBADF] The descriptor is not valid.

[EINVAL] Fd refers to a socket, not to a file.

[EROFS] The named file resides on a read-only file system.

RETURN VALUE

Upon successful completion, a value of 0 is returned. Otherwise, a value of −1 is returned and errno is set to indicate the error.

NOTE

The chmod function is defined in the 88open Binary and Object Compatibility Standards (BCS/OCS) for use in BCS/OCS compliant applications. The fchmod function is defined in the 88open BCS/OCS Networking Supplements (BCSNS/OCSNS) for use in BCS/OCS compliant networking applications. OCS/OCSNS-defined functions may be accessed by passing OCS options to cc(1) and ld(1).

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