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ACCESS(2)                  Linux Programmer's Manual                 ACCESS(2)

NAME
       access - check user's permissions for a file

SYNOPSIS
       #include <unistd.h>

       int access(const char *pathname, int mode);

DESCRIPTION
       access checks whether the process would be allowed to read, write or
       test for existence of the file (or other file system object) whose name
       is pathname.  If pathname is a symbolic link permissions of the file
       referred to by this symbolic link are tested.

       mode is a mask consisting of one or more of R_OK, W_OK, X_OK and F_OK.

       R_OK, W_OK and X_OK request checking whether the file exists and has
       read, write and execute permissions, respectively.  F_OK just requests
       checking for the existence of the file.

       The tests depend on the permissions of the directories occurring in the
       path to the file, as given in pathname, and on the permissions of
       directories and files referred to by symbolic links encountered on the
       way.

       The check is done with the process's real uid and gid, rather than with
       the effective ids as is done when actually attempting an operation.
       This is to allow set-UID programs to easily determine the invoking
       user's authority.

       Only access bits are checked, not the file type or contents.
       Therefore, if a directory is found to be "writable," it probably means
       that files can be created in the directory, and not that the directory
       can be written as a file.  Similarly, a DOS file may be found to be
       "executable," but the execve(2) call will still fail.

       If the process has appropriate privileges, an implementation may
       indicate success for X_OK even if none of the execute file permission
       bits are set.

RETURN VALUE
       On success (all requested permissions granted), zero is returned.  On
       error (at least one bit in mode asked for a permission that is denied,
       or some other error occurred), -1 is returned, and errno is set
       appropriately.

ERRORS
       access shall fail if:

       EACCES The requested access would be denied to the file or search
              permission is denied to one of the directories in pathname.

       ELOOP  Too many symbolic links were encountered in resolving pathname.

       ENAMETOOLONG
              pathname is too long.

       ENOENT A directory component in pathname would have been accessible but
              does not exist or was a dangling symbolic link.

       ENOTDIR
              A component used as a directory in pathname is not, in fact, a
              directory.

       EROFS  Write permission was requested for a file on a read-only
              filesystem.

       access may fail if:

       EFAULT pathname points outside your accessible address space.

       EINVAL mode was incorrectly specified.

       EIO    An I/O error occurred.

       ENOMEM Insufficient kernel memory was available.

       ETXTBSY
              Write access was requested to an executable which is being
              executed.

RESTRICTIONS
       access returns an error if any of the access types in the requested
       call fails, even if other types might be successful.

       access may not work correctly on NFS file systems with UID mapping
       enabled, because UID mapping is done on the server and hidden from the
       client, which checks permissions.

       Using access to check if a user is authorized to e.g. open a file
       before actually doing so using open(2) creates a security hole, because
       the user might exploit the short time interval between checking and
       opening the file to manipulate it.

CONFORMING TO
       SVID, AT&T, POSIX, X/OPEN, BSD 4.3

SEE ALSO
       stat(2), open(2), chmod(2), chown(2), setuid(2), setgid(2)

Linux                             2002-04-23                         ACCESS(2)

NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | RESTRICTIONS | CONFORMING TO | SEE ALSO

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