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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 November 11, 2018 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_BENEATH 124Only operate on files and directories below the topping directory. 125See the description of the 126.Dv O_BENEATH 127flag in the 128.Xr open 2 129manual page. 130.El 131.Pp 132Even if a process's real or effective user has appropriate privileges 133and indicates success for 134.Dv X_OK , 135the file may not actually have execute permission bits set. 136Likewise for 137.Dv R_OK 138and 139.Dv W_OK . 140.Sh RETURN VALUES 141.Rv -std 142.Sh ERRORS 143.Fn access , 144.Fn eaccess , 145or 146.Fn faccessat 147will fail if: 148.Bl -tag -width Er 149.It Bq Er EINVAL 150The value of the 151.Fa mode 152argument is invalid. 153.It Bq Er ENOTDIR 154A component of the path prefix is not a directory. 155.It Bq Er ENAMETOOLONG 156A component of a pathname exceeded 255 characters, 157or an entire path name exceeded 1023 characters. 158.It Bq Er ENOENT 159The named file does not exist. 160.It Bq Er ELOOP 161Too many symbolic links were encountered in translating the pathname. 162.It Bq Er EROFS 163Write access is requested for a file on a read-only file system. 164.It Bq Er ETXTBSY 165Write access is requested for a pure procedure (shared text) 166file presently being executed. 167.It Bq Er EACCES 168Permission bits of the file mode do not permit the requested 169access, or search permission is denied on a component of the 170path prefix. 171.It Bq Er EFAULT 172The 173.Fa path 174argument 175points outside the process's allocated address space. 176.It Bq Er EIO 177An I/O error occurred while reading from or writing to the file system. 178.El 179.Pp 180Also, the 181.Fn faccessat 182system call may fail if: 183.Bl -tag -width Er 184.It Bq Er EBADF 185The 186.Fa path 187argument does not specify an absolute path and the 188.Fa fd 189argument is 190neither 191.Dv AT_FDCWD 192nor a valid file descriptor. 193.It Bq Er EINVAL 194The value of the 195.Fa flag 196argument is not valid. 197.It Bq Er ENOTDIR 198The 199.Fa path 200argument is not an absolute path and 201.Fa fd 202is neither 203.Dv AT_FDCWD 204nor a file descriptor associated with a directory. 205.It Bq Er ENOTCAPABLE 206.Fa path 207is an absolute path, 208or contained a ".." component leading to a 209directory outside of the directory hierarchy specified by 210.Fa fd , 211and the process is in capability mode. 212.It Bq Er ENOTCAPABLE 213The 214.Dv AT_BENEATH 215flag was provided to 216.Fn faccessat , 217and the absolute 218.Fa path 219does not have its tail fully contained under the topping directory, 220or the relative 221.Fa path 222escapes it. 223.El 224.Sh SEE ALSO 225.Xr chmod 2 , 226.Xr intro 2 , 227.Xr stat 2 228.Sh STANDARDS 229The 230.Fn access 231system call is expected to conform to 232.St -p1003.1-90 . 233The 234.Fn faccessat 235system call follows The Open Group Extended API Set 2 specification. 236.Sh HISTORY 237The 238.Fn access 239function appeared in 240.At v7 . 241The 242.Fn faccessat 243system call appeared in 244.Fx 8.0 . 245.Sh SECURITY CONSIDERATIONS 246The 247.Fn access 248system call 249is a potential security hole due to race conditions and 250should never be used. 251Set-user-ID and set-group-ID applications should restore the 252effective user or group ID, 253and perform actions directly rather than use 254.Fn access 255to simulate access checks for the real user or group ID. 256The 257.Fn eaccess 258system call 259likewise may be subject to races if used inappropriately. 260.Pp 261.Fn access 262remains useful for providing clues to users as to whether operations 263make sense for particular filesystem objects (e.g. 'delete' menu 264item only highlighted in a writable folder ... avoiding interpretation 265of the st_mode bits that the application might not understand -- 266e.g. in the case of AFS). 267It also allows a cheaper file existence test than 268.Xr stat 2 . 269