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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, 2020 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.It Bq Er EINTEGRITY 179Corrupted data was detected while reading from the file system. 180.El 181.Pp 182Also, the 183.Fn faccessat 184system call may fail if: 185.Bl -tag -width Er 186.It Bq Er EBADF 187The 188.Fa path 189argument does not specify an absolute path and the 190.Fa fd 191argument is 192neither 193.Dv AT_FDCWD 194nor a valid file descriptor. 195.It Bq Er EINVAL 196The value of the 197.Fa flag 198argument is not valid. 199.It Bq Er ENOTDIR 200The 201.Fa path 202argument is not an absolute path and 203.Fa fd 204is neither 205.Dv AT_FDCWD 206nor a file descriptor associated with a directory. 207.It Bq Er ENOTCAPABLE 208.Fa path 209is an absolute path, 210or contained a ".." component leading to a 211directory outside of the directory hierarchy specified by 212.Fa fd , 213and the process is in capability mode. 214.It Bq Er ENOTCAPABLE 215The 216.Dv AT_BENEATH 217flag was provided to 218.Fn faccessat , 219and the absolute 220.Fa path 221does not have its tail fully contained under the topping directory, 222or the relative 223.Fa path 224escapes it. 225.El 226.Sh SEE ALSO 227.Xr chmod 2 , 228.Xr intro 2 , 229.Xr stat 2 230.Sh STANDARDS 231The 232.Fn access 233system call is expected to conform to 234.St -p1003.1-90 . 235The 236.Fn faccessat 237system call follows The Open Group Extended API Set 2 specification. 238.Sh HISTORY 239The 240.Fn access 241function appeared in 242.At v7 . 243The 244.Fn faccessat 245system call appeared in 246.Fx 8.0 . 247.Sh SECURITY CONSIDERATIONS 248The 249.Fn access 250system call 251is a potential security hole due to race conditions and 252should never be used. 253Set-user-ID and set-group-ID applications should restore the 254effective user or group ID, 255and perform actions directly rather than use 256.Fn access 257to simulate access checks for the real user or group ID. 258The 259.Fn eaccess 260system call 261likewise may be subject to races if used inappropriately. 262.Pp 263.Fn access 264remains useful for providing clues to users as to whether operations 265make sense for particular filesystem objects (e.g. 'delete' menu 266item only highlighted in a writable folder ... avoiding interpretation 267of the st_mode bits that the application might not understand -- 268e.g. in the case of AFS). 269It also allows a cheaper file existence test than 270.Xr stat 2 . 271