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ACCESS(2) FreeBSD System Calls Manual ACCESS(2)
NAME
access, eaccess, faccessat - 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);
int
faccessat(int fd, const char *path, int mode, int flag);
DESCRIPTION
The access() and eaccess() system calls check the accessibility 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 permission, W_OK
for write permission, and X_OK for execute/search permission), 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.
The faccessat() system call is equivalent to access() except in the case
where path specifies a relative path. In this case the file whose
accessibility is to be determined is located relative to the directory
associated with the file descriptor fd instead of the current working
directory. If faccessat() is passed the special value AT_FDCWD in the fd
parameter, the current working directory is used and the behavior is
identical to a call to access(). Values for flag are constructed by a
bitwise-inclusive OR of flags from the following list, defined in
<fcntl.h>:
AT_EACCESS
The checks for accessibility are performed using the effective
user and group IDs instead of the real user and group ID as
required in a call to access().
AT_RESOLVE_BENEATH
Only walk paths below the directory specified by the fd
descriptor. See the description of the O_RESOLVE_BENEATH flag in
the open(2) manual page.
AT_EMPTY_PATH
If the path argument is an empty string, operate on the file or
directory referenced by the descriptor fd. If fd is equal to
Upon successful completion, the value 0 is returned; otherwise the
value -1 is returned and the global variable errno is set to indicate the
error.
ERRORS
access(), eaccess(), or faccessat() will fail if:
[EINVAL] The value of the mode argument is invalid.
[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 characters.
[ENOENT] The named file does not exist.
[ELOOP] Too many symbolic links were encountered in
translating the pathname.
[EROFS] Write access is requested for a file on a read-only
file system.
[ETXTBSY] Write access is requested for a pure procedure (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 process's
allocated address space.
[EIO] An I/O error occurred while reading from or writing to
the file system.
[EINTEGRITY] Corrupted data was detected while reading from the
file system.
Also, the faccessat() system call may fail if:
[EBADF] The path argument does not specify an absolute path
and the fd argument is neither AT_FDCWD nor a valid
file descriptor.
[EINVAL] The value of the flag argument is not valid.
[ENOTDIR] The path argument is not an absolute path and fd is
neither AT_FDCWD nor a file descriptor associated with
a directory.
[ENOTCAPABLE] path is an absolute path, or contained a ".."
component leading to a directory outside of the
directory hierarchy specified by fd, and the process
is in capability mode.
SEE ALSO
chmod(2), intro(2), stat(2)
STANDARDS
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.
access() remains useful for providing clues to users as to whether
operations make sense for particular filesystem objects (e.g. 'delete'
menu item only highlighted in a writable folder ... avoiding
interpretation of the st_mode bits that the application might not
understand -- e.g. in the case of AFS). It also allows a cheaper file
existence test than stat(2).
FreeBSD 14.0-RELEASE-p11 March 30, 2021 FreeBSD 14.0-RELEASE-p11