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@(#)access.2 8.2 (Berkeley) 4/1/94
.Dd April 30, 2010 .Dt ACCESS 2 .Os .Sh NAME .Nm access .Nd check access permissions of a file or pathname .Sh LIBRARY .Lb libc .Sh SYNOPSIS n unistd.h .Ft int .Fn access "const char *path" "int mode" .Sh DESCRIPTION The .Fn access function checks the accessibility of the file named by .Fa path for the access permissions indicated by .Fa mode . The value of .Fa mode is the bitwise inclusive OR of the access permissions to be checked
f ( Dv R_OK for read permission, .Dv W_OK for write permission and .Dv X_OK for execute/search permission) or the existence test, .Dv F_OK . All components of the pathname .Fa path are checked for access permissions (including .Dv F_OK ) .
p The real user ID is used in place of the effective user ID and the real group access list (including the real group ID) are used in place of the effective ID for verifying permission.
p If a process has super-user privileges and indicates success for .Dv R_OK or .Dv W_OK , the file may not actually have read or write permission bits set. If a process has super-user privileges and indicates success for .Dv X_OK , at least one of the user, group, or other execute bits is set. (However, the file may still not be executable. See .Xr execve 2 . ) .Sh RETURN VALUES If .Fa path cannot be found or if any of the desired access modes would not be granted, then a -1 value is returned; otherwise a 0 value is returned. .Sh ERRORS Access to the file is denied if: l -tag -width Er t Bq Er EACCES Permission bits of the file mode do not permit the requested access, or search permission is denied on a component of the path prefix. The owner of a file has permission checked with respect to the .Dq owner read, write, and execute mode bits, members of the file's group other than the owner have permission checked with respect to the .Dq group mode bits, and all others have permissions checked with respect to the .Dq other mode bits. t Bq Er EFAULT .Fa path points outside the process's allocated address space. t Bq Er EIO An I/O error occurred while reading from or writing to the file system. t Bq Er ELOOP Too many symbolic links were encountered in translating the pathname. t Bq Er ENAMETOOLONG A component of a pathname exceeded rq Dv NAME_MAX characters, or an entire path name exceeded rq Dv PATH_MAX characters. t Bq Er ENOENT The named file does not exist. t Bq Er ENOTDIR A component of the path prefix is not a directory. t Bq Er EROFS Write access is requested for a file on a read-only file system. t Bq Er ETXTBSY Write access is requested for a pure procedure (shared text) file presently being executed. .El .Sh SEE ALSO .Xr chmod 2 , .Xr execve 2 , .Xr stat 2 .Sh STANDARDS The .Fn access function conforms to .St -p1003.1-90 . .Sh SECURITY CONSIDERATIONS The .Fn access system call is a potential security hole due to race conditions. It should never be used. Set-user-ID and set-group-ID applications should restore the effective user or group ID, and perform actions directly rather than use .Fn access to simulate access checks for the real user or group ID. The .Fn eaccess system call likewise may be subject to races if used inappropriately.
p The .Fn access system call may however have some value in providing clues to users as to whether certain operations make sense for a particular filesystem object. Arguably it also allows a cheaper file existence test than .Xr stat 2 .
Indexes created Sun Oct 12 09:09:55 GMT 2025