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Neither the name of the University nor the names of its contributors 13.\" may be used to endorse or promote products derived from this software 14.\" without specific prior written permission. 15.\" 16.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 17.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 18.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 19.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 20.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 21.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 22.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 23.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 24.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 25.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 26.\" SUCH DAMAGE. 27.\" 28.\" @(#)access.2 8.2 (Berkeley) 4/1/94 29.\" $FreeBSD$ 30.\" 31.Dd March 30, 2021 32.Dt ACCESS 2 33.Os 34.Sh NAME 35.Nm access , 36.Nm eaccess , 37.Nm faccessat 38.Nd check accessibility of a file 39.Sh LIBRARY 40.Lb libc 41.Sh SYNOPSIS 42.In unistd.h 43.Ft int 44.Fn access "const char *path" "int mode" 45.Ft int 46.Fn eaccess "const char *path" "int mode" 47.Ft int 48.Fn faccessat "int fd" "const char *path" "int mode" "int flag" 49.Sh DESCRIPTION 50The 51.Fn access 52and 53.Fn eaccess 54system calls check the accessibility of the 55file named by 56the 57.Fa path 58argument 59for the access permissions indicated by 60the 61.Fa mode 62argument. 63The value of 64.Fa mode 65is either the bitwise-inclusive OR of the access permissions to be 66checked 67.Dv ( R_OK 68for read permission, 69.Dv W_OK 70for write permission, and 71.Dv X_OK 72for execute/search permission), 73or the existence test 74.Pq Dv F_OK . 75.Pp 76For additional information, see the 77.Sx "File Access Permission" 78section of 79.Xr intro 2 . 80.Pp 81The 82.Fn eaccess 83system call uses 84the effective user ID and the group access list 85to authorize the request; 86the 87.Fn access 88system call uses 89the real user ID in place of the effective user ID, 90the real group ID in place of the effective group ID, 91and the rest of the group access list. 92.Pp 93The 94.Fn faccessat 95system call is equivalent to 96.Fn access 97except in the case where 98.Fa path 99specifies a relative path. 100In this case the file whose accessibility is to be determined is 101located relative to the directory associated with the file descriptor 102.Fa fd 103instead of the current working directory. 104If 105.Fn faccessat 106is passed the special value 107.Dv AT_FDCWD 108in the 109.Fa fd 110parameter, the current working directory is used and the behavior is 111identical to a call to 112.Fn access . 113Values for 114.Fa flag 115are constructed by a bitwise-inclusive OR of flags from the following 116list, defined in 117.In fcntl.h : 118.Bl -tag -width indent 119.It Dv AT_EACCESS 120The checks for accessibility are performed using the effective user and group 121IDs instead of the real user and group ID as required in a call to 122.Fn access . 123.It Dv AT_RESOLVE_BENEATH 124Only walk paths below the directory specified by the 125.Ar fd 126descriptor. 127See the description of the 128.Dv O_RESOLVE_BENEATH 129flag in the 130.Xr open 2 131manual page. 132.It Dv AT_EMPTY_PATH 133If the 134.Fa path 135argument is an empty string, operate on the file or directory 136referenced by the descriptor 137.Fa fd . 138If 139.Fa fd 140is equal to 141.Dv AT_FDCWD , 142operate on the current working directory. 143.El 144.Pp 145Even if a process's real or effective user has appropriate privileges 146and indicates success for 147.Dv X_OK , 148the file may not actually have execute permission bits set. 149Likewise for 150.Dv R_OK 151and 152.Dv W_OK . 153.Sh RETURN VALUES 154.Rv -std 155.Sh ERRORS 156.Fn access , 157.Fn eaccess , 158or 159.Fn faccessat 160will fail if: 161.Bl -tag -width Er 162.It Bq Er EINVAL 163The value of the 164.Fa mode 165argument is invalid. 166.It Bq Er ENOTDIR 167A component of the path prefix is not a directory. 168.It Bq Er ENAMETOOLONG 169A component of a pathname exceeded 255 characters, 170or an entire path name exceeded 1023 characters. 171.It Bq Er ENOENT 172The named file does not exist. 173.It Bq Er ELOOP 174Too many symbolic links were encountered in translating the pathname. 175.It Bq Er EROFS 176Write access is requested for a file on a read-only file system. 177.It Bq Er ETXTBSY 178Write access is requested for a pure procedure (shared text) 179file presently being executed. 180.It Bq Er EACCES 181Permission bits of the file mode do not permit the requested 182access, or search permission is denied on a component of the 183path prefix. 184.It Bq Er EFAULT 185The 186.Fa path 187argument 188points outside the process's allocated address space. 189.It Bq Er EIO 190An I/O error occurred while reading from or writing to the file system. 191.It Bq Er EINTEGRITY 192Corrupted data was detected while reading from the file system. 193.El 194.Pp 195Also, the 196.Fn faccessat 197system call may fail if: 198.Bl -tag -width Er 199.It Bq Er EBADF 200The 201.Fa path 202argument does not specify an absolute path and the 203.Fa fd 204argument is 205neither 206.Dv AT_FDCWD 207nor a valid file descriptor. 208.It Bq Er EINVAL 209The value of the 210.Fa flag 211argument is not valid. 212.It Bq Er ENOTDIR 213The 214.Fa path 215argument is not an absolute path and 216.Fa fd 217is neither 218.Dv AT_FDCWD 219nor a file descriptor associated with a directory. 220.It Bq Er ENOTCAPABLE 221.Fa path 222is an absolute path, 223or contained a ".." component leading to a 224directory outside of the directory hierarchy specified by 225.Fa fd , 226and the process is in capability mode. 227.El 228.Sh SEE ALSO 229.Xr chmod 2 , 230.Xr intro 2 , 231.Xr stat 2 232.Sh STANDARDS 233The 234.Fn access 235system call is expected to conform to 236.St -p1003.1-90 . 237The 238.Fn faccessat 239system call follows The Open Group Extended API Set 2 specification. 240.Sh HISTORY 241The 242.Fn access 243function appeared in 244.At v7 . 245The 246.Fn faccessat 247system call appeared in 248.Fx 8.0 . 249.Sh SECURITY CONSIDERATIONS 250The 251.Fn access 252system call 253is a potential security hole due to race conditions and 254should never be used. 255Set-user-ID and set-group-ID applications should restore the 256effective user or group ID, 257and perform actions directly rather than use 258.Fn access 259to simulate access checks for the real user or group ID. 260The 261.Fn eaccess 262system call 263likewise may be subject to races if used inappropriately. 264.Pp 265.Fn access 266remains useful for providing clues to users as to whether operations 267make sense for particular filesystem objects (e.g. 'delete' menu 268item only highlighted in a writable folder ... avoiding interpretation 269of the st_mode bits that the application might not understand -- 270e.g. in the case of AFS). 271It also allows a cheaper file existence test than 272.Xr stat 2 . 273