#include <unistd.h>int access(const char *path, int amode);
The access() function checks the file named by the pathname pointed to by the path argument for accessibility according to the bit pattern contained in amode, using the real user ID in place of the effective user ID and the real group ID in place of the effective group ID. This allows a setuid process to verify that the user running it would have had permission to access this file.
The value of amode is either the bitwise inclusive OR of the access permissions to be checked (R_OK, W_OK, X_OK) or the existence test, F_OK.
These constants are defined in <unistd.h> as follows:
Test for read permission.
Test for write permission.
Test for execute or search permission.
Check existence of file
See intro(2) for additional information about "File Access Permission".
If any access permissions are to be checked, each will be checked individually, as described in intro(2). If the process has appropriate privileges, an implementation may indicate success for X_OK even if none of the execute file permission bits are set.
If the requested access is permitted, access() succeeds and returns 0. Otherwise, -1 is returned and errno is set to indicate the error.
The access() function will fail if:
Permission bits of the file mode do not permit the requested access, or search permission is denied on a component of the path prefix.
path points to an illegal address.
A signal was caught during the access() function.
Too many symbolic links were encountered in resolving path.
The length of the path argument exceeds PATH_MAX, or a pathname component is longer than NAME_MAX while _POSIX_NO_TRUNC is in effect.
A component of path does not name an existing file or path is an empty string.
path points to a remote machine and the link to that machine is no longer active.
A component of the path prefix is not a directory.
Write access is requested for a file on a read-only file system.
The access() function may fail if:
The value of the amode argument is invalid.
Pathname resolution of a symbolic link produced an intermediate result whose length exceeds PATH_MAX.
Write access is requested for a pure procedure (shared text) file that is being executed.
Additional values of amode other than the set defined in the description may be valid, for example, if a system has extended access controls.
See attributes(5) for descriptions of the following attributes:
|ATTRIBUTE TYPE||ATTRIBUTE VALUE|