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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.\" 30.Dd May 21, 2024 31.Dt ACCESS 2 32.Os 33.Sh NAME 34.Nm access , 35.Nm eaccess , 36.Nm faccessat 37.Nd check accessibility of a file 38.Sh LIBRARY 39.Lb libc 40.Sh SYNOPSIS 41.In unistd.h 42.Ft int 43.Fn access "const char *path" "int mode" 44.Ft int 45.Fn eaccess "const char *path" "int mode" 46.Ft int 47.Fn faccessat "int fd" "const char *path" "int mode" "int flag" 48.Sh DESCRIPTION 49The 50.Fn access , 51.Fn eaccess 52and 53.Fn faccessat 54system calls report whether an attempt to access the file designated 55by their 56.Fa path 57in the manner described by their 58.Fa mode 59argument is likely to succeed. 60The value of 61.Fa mode 62is either the bitwise-inclusive OR of the desired permissions 63.Po 64.Dv R_OK 65for read permission, 66.Dv W_OK 67for write permission, and 68.Dv X_OK 69for execute / search permission 70.Pc 71or 72.Dv F_OK 73to simply check whether the file exists. 74.Pp 75For a number of reasons, these system calls cannot be relied upon to 76give a correct and definitive answer. 77They can at best provide an early indication of the expected outcome, 78to be confirmed by actually attempting the operation. 79For existence checks, either 80.Xr stat 2 81or 82.Xr lstat 2 83should be used instead. 84See also 85.Sx SECURITY CONSIDERATIONS 86below. 87.Pp 88The 89.Fn eaccess 90system call uses 91the effective user ID and the group access list 92to authorize the request; 93the 94.Fn access 95system call uses 96the real user ID in place of the effective user ID, 97the real group ID in place of the effective group ID, 98and the rest of the group access list. 99.Pp 100See the 101.Sx DEFINITIONS 102section of 103.Xr intro 2 104for additional information on file access permissions and real 105vs. effective user and group IDs. 106.Pp 107The 108.Fn faccessat 109system call is equivalent to 110.Fn access 111except in the case where 112.Fa path 113specifies a relative path. 114In this case the file whose accessibility is to be determined is 115located relative to the directory associated with the file descriptor 116.Fa fd 117instead of the current working directory. 118If 119.Fn faccessat 120is passed the special value 121.Dv AT_FDCWD 122in the 123.Fa fd 124parameter, the current working directory is used and the behavior is 125identical to a call to 126.Fn access . 127Values for 128.Fa flag 129are constructed by a bitwise-inclusive OR of flags from the following 130list, defined in 131.In fcntl.h : 132.Bl -tag -width indent 133.It Dv AT_EACCESS 134The checks are performed using the effective user and group IDs, 135like 136.Fn eaccess , 137instead of the real user and group ID, like 138.Fn access . 139.It Dv AT_RESOLVE_BENEATH 140Only walk paths below the directory specified by the 141.Ar fd 142descriptor. 143See the description of the 144.Dv O_RESOLVE_BENEATH 145flag in the 146.Xr open 2 147manual page. 148.It Dv AT_EMPTY_PATH 149If the 150.Fa path 151argument is an empty string, operate on the file or directory 152referenced by the descriptor 153.Fa fd . 154If 155.Fa fd 156is equal to 157.Dv AT_FDCWD , 158operate on the current working directory. 159.El 160.Pp 161Even if a process's real or effective user has appropriate privileges 162and indicates success for 163.Dv X_OK , 164the file may not actually have execute permission bits set. 165Likewise for 166.Dv R_OK 167and 168.Dv W_OK . 169.Sh RETURN VALUES 170.Rv -std 171.Sh ERRORS 172The 173.Fn access , 174.Fn eaccess , 175and 176.Fn faccessat 177system calls may fail if: 178.Bl -tag -width Er 179.It Bq Er EINVAL 180The value of the 181.Fa mode 182argument is invalid. 183.It Bq Er ENOTDIR 184A component of the path prefix is not a directory. 185.It Bq Er ENAMETOOLONG 186A component of a pathname exceeded 255 characters, 187or an entire path name exceeded 1023 characters. 188.It Bq Er ENOENT 189The named file does not exist. 190.It Bq Er ELOOP 191Too many symbolic links were encountered in translating the pathname. 192.It Bq Er EROFS 193Write access is requested for a file on a read-only file system. 194.It Bq Er ETXTBSY 195Write access is requested for a pure procedure (shared text) 196file presently being executed. 197.It Bq Er EACCES 198Permission bits of the file mode do not permit the requested 199access, or search permission is denied on a component of the 200path prefix. 201.It Bq Er EFAULT 202The 203.Fa path 204argument 205points outside the process's allocated address space. 206.It Bq Er EIO 207An I/O error occurred while reading from or writing to the file system. 208.It Bq Er EINTEGRITY 209Corrupted data was detected while reading from the file system. 210.El 211.Pp 212Also, the 213.Fn faccessat 214system call may fail if: 215.Bl -tag -width Er 216.It Bq Er EBADF 217The 218.Fa path 219argument does not specify an absolute path and the 220.Fa fd 221argument is 222neither 223.Dv AT_FDCWD 224nor a valid file descriptor. 225.It Bq Er EINVAL 226The value of the 227.Fa flag 228argument is not valid. 229.It Bq Er ENOTDIR 230The 231.Fa path 232argument is not an absolute path and 233.Fa fd 234is neither 235.Dv AT_FDCWD 236nor a file descriptor associated with a directory. 237.It Bq Er ENOTCAPABLE 238.Fa path 239is an absolute path, 240or contained a ".." component leading to a 241directory outside of the directory hierarchy specified by 242.Fa fd , 243and the process is in capability mode. 244.El 245.Sh SEE ALSO 246.Xr chmod 2 , 247.Xr intro 2 , 248.Xr stat 2 249.Sh STANDARDS 250The 251.Fn access 252system call is expected to conform to 253.St -p1003.1-90 . 254The 255.Fn faccessat 256system call follows The Open Group Extended API Set 2 specification. 257.Sh HISTORY 258The 259.Fn access 260function appeared in 261.At v7 . 262The 263.Fn faccessat 264system call appeared in 265.Fx 8.0 . 266.Sh SECURITY CONSIDERATIONS 267The 268.Fn access , 269.Fn eaccess , 270and 271.Fn faccessat 272system calls are subject to time-of-check-to-time-of-use races and 273should not be relied upon for file permission enforcement purposes. 274Instead, applications should perform the desired action using the 275requesting user's credentials. 276