ACCESS(2)
NAME
access − determine if a file can be accessed
USAGE
#include <sys/file.h>
#define R_OK4 /* test for read permission */
#define W_OK2 /* test for write permission */
#define X_OK1 /* test for execute (search) permission */
#define F_OK0 /* test for presence of file */
accessible = access(path, mode)
int accessible;
char *path;
int mode;
DESCRIPTION
Access checks the given file path for access rights according to mode, which is an ‘inclusive or’ of the bits R_OK, W_OK and X_OK. Specifying mode as F_OK (i.e., zero) tests whether the directories leading to the file can be searched and whether the file exists.
Access uses the real user ID and the group access list (including the real group ID) to verify permission, so this call is useful to set-UID programs.
Note that access only checks access bits. A directory may appear writable according to access, but an attempt to open it for writing will fail (although files may be created there); a file may look executable, but execve will fail unless the file is in the proper format.
RETURN VALUE
If path cannot be found or if any of the desired access modes would not be granted, then a −1 value is returned; otherwise, access returns a zero.
ERRORS
Access to the file is denied if one or more of the following are true:
[ENOTDIR] A component of the path prefix is not a directory.
[ENOENT] The argument pathname was too long.
[ENOENT] Read, write, or execute (search) permission is requested for a null pathname, or the named file does not exist.
[EPERM] The argument contains a byte with the high-order bit set.
[ELOOP] The call encountered too many symbolic links in translating the pathname.
[EROFS] Write access is requested for a file on a read-only file system.
[EACCES] Permission bits of the file mode do not permit the requested access; or search permission is denied on a component of the path prefix. The owner of a file has permission checked with respect to the “owner” read, write, and execute mode bits. Members of the file’s group (other than the owner) have permission checked with respect to the “group” mode bits, and all others have permissions checked with respect to the “other” mode bits.
[EFAULT] Path points outside the process’ allocated address space.