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(), eaccess() and faccessat() system calls report whether an
attempt to access the file designated by their path in the manner
described by their mode argument is likely to succeed. The value of mode
is either the bitwise-inclusive OR of the desired permissions (R_OK for
read permission, W_OK for write permission, and X_OK for execute / search
permission) or F_OK to simply check whether the file exists.
For a number of reasons, these system calls cannot be relied upon to give
a correct and definitive answer. They can at best provide an early
indication of the expected outcome, to be confirmed by actually
attempting the operation. For existence checks, either stat(2) or
lstat(2) should be used instead. See also SECURITY CONSIDERATIONS below.
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.
See the DEFINITIONS section of intro(2) for additional information on
file access permissions and real vs. effective user and group IDs.
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 are performed using the effective user and group IDs,
like eaccess(), instead of the real user and group ID, like
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
AT_FDCWD, operate on the current working directory.
AT_SYMLINK_NOFOLLOW
If path names a symbolic link, access of the symbolic link is
evaluated.
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
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
The access(), eaccess(), and faccessat() system calls may 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
The access() system call is expected to conform to IEEE Std 1003.1-1990
("POSIX.1"). The faccessat() system call follows The Open Group Extended
API Set 2 specification.
HISTORY
The access() function appeared in Version 7 AT&T UNIX. The faccessat()
system call appeared in FreeBSD 8.0.
SECURITY CONSIDERATIONS
The access(), eaccess(), and faccessat() system calls are subject to
time-of-check-to-time-of-use races and should not be relied upon for file
permission enforcement purposes. Instead, applications should perform
the desired action using the requesting user's credentials.
FreeBSD 15.1-STABLE-HBSD August 11, 2024 ACCESS(2)