access(2)

NAME

access, eaccess - check accessibility of a file

LIBRARY

Standard C Library (libc, -lc)

SYNOPSIS

#include <unistd.h>
int
access(const char *path, int mode);
int
eaccess(const char *path, int mode);

DESCRIPTION

The access() and eaccess() system calls check the accessi

bility of the
file named by the path argument for the access permissions

indicated by
the mode argument. The value of mode is either the bitwise

inclusive OR
of the access permissions to be checked (R_OK for read per

mission, W_OK
for write permission, and X_OK for execute/search permis

sion), or the
existence test (F_OK).

For additional information, see the File Access Permission

section of
intro(2).

The eaccess() system call uses the effective user ID and the

group access
list to authorize the request; the access() system call uses

the real
user ID in place of the effective user ID, the real group ID

in place of
the effective group ID, and the rest of the group access

list.

Even if a process's real or effective user has appropriate

privileges and
indicates success for X_OK, the file may not actually have

execute permission bits set. Likewise for R_OK and W_OK.

RETURN VALUES

The function returns the value 0 if successful; otherwise

the value -1 is
returned and the global variable errno is set to indicate

the error.

ERRORS

Access to the file is denied if:

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

directory.

[ENAMETOOLONG] A component of a pathname exceeded 255

characters, or

an entire path name exceeded 1023 charac

ters.

[ENOENT] The named file does not exist.

[ELOOP] Too many symbolic links were encountered

in translat

ing the pathname.

[EROFS] Write access is requested for a file on a

read-only

file system.

[ETXTBSY] Write access is requested for a pure pro

cedure (shared

text) file presently being executed.

[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.

[EFAULT] The path argument points outside the pro

cess's allo

cated address space.

[EIO] An I/O error occurred while reading from

or writing to

the file system.

SECURITY CONSIDERATIONS

The access() system call is a potential security hole due to

race conditions and should never be used. Set-user-ID and set-group

ID applications should restore the effective user or group ID, and

perform actions
directly rather than use access() to simulate access checks

for the real
user or group ID. The eaccess() system call likewise may be

subject to
races if used inappropriately.

SEE ALSO

chmod(2), intro(2), stat(2)

STANDARDS

The access() system call is expected to conform to ISO/IEC

9945-1:1990
(``POSIX.1'').

HISTORY

The access() function appeared in Version 7 AT&T UNIX.

BSD September 21, 2001

BSD