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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 February 23, 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.El 133.Pp 134Even if a process's real or effective user has appropriate privileges 135and indicates success for 136.Dv X_OK , 137the file may not actually have execute permission bits set. 138Likewise for 139.Dv R_OK 140and 141.Dv W_OK . 142.Sh RETURN VALUES 143.Rv -std 144.Sh ERRORS 145.Fn access , 146.Fn eaccess , 147or 148.Fn faccessat 149will fail if: 150.Bl -tag -width Er 151.It Bq Er EINVAL 152The value of the 153.Fa mode 154argument is invalid. 155.It Bq Er ENOTDIR 156A component of the path prefix is not a directory. 157.It Bq Er ENAMETOOLONG 158A component of a pathname exceeded 255 characters, 159or an entire path name exceeded 1023 characters. 160.It Bq Er ENOENT 161The named file does not exist. 162.It Bq Er ELOOP 163Too many symbolic links were encountered in translating the pathname. 164.It Bq Er EROFS 165Write access is requested for a file on a read-only file system. 166.It Bq Er ETXTBSY 167Write access is requested for a pure procedure (shared text) 168file presently being executed. 169.It Bq Er EACCES 170Permission bits of the file mode do not permit the requested 171access, or search permission is denied on a component of the 172path prefix. 173.It Bq Er EFAULT 174The 175.Fa path 176argument 177points outside the process's allocated address space. 178.It Bq Er EIO 179An I/O error occurred while reading from or writing to the file system. 180.It Bq Er EINTEGRITY 181Corrupted data was detected while reading from the file system. 182.El 183.Pp 184Also, the 185.Fn faccessat 186system call may fail if: 187.Bl -tag -width Er 188.It Bq Er EBADF 189The 190.Fa path 191argument does not specify an absolute path and the 192.Fa fd 193argument is 194neither 195.Dv AT_FDCWD 196nor a valid file descriptor. 197.It Bq Er EINVAL 198The value of the 199.Fa flag 200argument is not valid. 201.It Bq Er ENOTDIR 202The 203.Fa path 204argument is not an absolute path and 205.Fa fd 206is neither 207.Dv AT_FDCWD 208nor a file descriptor associated with a directory. 209.It Bq Er ENOTCAPABLE 210.Fa path 211is an absolute path, 212or contained a ".." component leading to a 213directory outside of the directory hierarchy specified by 214.Fa fd , 215and the process is in capability mode. 216.El 217.Sh SEE ALSO 218.Xr chmod 2 , 219.Xr intro 2 , 220.Xr stat 2 221.Sh STANDARDS 222The 223.Fn access 224system call is expected to conform to 225.St -p1003.1-90 . 226The 227.Fn faccessat 228system call follows The Open Group Extended API Set 2 specification. 229.Sh HISTORY 230The 231.Fn access 232function appeared in 233.At v7 . 234The 235.Fn faccessat 236system call appeared in 237.Fx 8.0 . 238.Sh SECURITY CONSIDERATIONS 239The 240.Fn access 241system call 242is a potential security hole due to race conditions and 243should never be used. 244Set-user-ID and set-group-ID applications should restore the 245effective user or group ID, 246and perform actions directly rather than use 247.Fn access 248to simulate access checks for the real user or group ID. 249The 250.Fn eaccess 251system call 252likewise may be subject to races if used inappropriately. 253.Pp 254.Fn access 255remains useful for providing clues to users as to whether operations 256make sense for particular filesystem objects (e.g. 'delete' menu 257item only highlighted in a writable folder ... avoiding interpretation 258of the st_mode bits that the application might not understand -- 259e.g. in the case of AFS). 260It also allows a cheaper file existence test than 261.Xr stat 2 . 262