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Annotated edit history of access(2) version 2, including all changes. View license author blame.
Rev Author # Line
1 perry 1 ACCESS
2 !!!ACCESS
2 PerryLorier 3
1 perry 4 ----
5 !!NAME
6
7
8 access - check user's permissions for a file
9 !!SYNOPSIS
10
11
2 PerryLorier 12 __#include <unistd.h>__
13 __access(char *__''pathname''__, int__ ''mode''__);__
14
1 perry 15 !!DESCRIPTION
16
17 __access__ checks whether the process would be allowed to
18 read, write or test for existence of the file (or other file
2 PerryLorier 19 system object) whose name is ''pathname''. If ''pathname'' is a symbolic link permissions of the filereferred to by this symbolic link are tested.
1 perry 20
2 PerryLorier 21 ''mode'' is a mask consisting of one or more of __R_OK__, __W_OK__, __X_OK__ and __F_OK__.
1 perry 22
23
24 __R_OK__, __W_OK__ and __X_OK__ request checking
25 whether the file exists and has read, write and execute
26 permissions, respectively. __F_OK__ just requests
27 checking for the existence of the file.
28
29 The tests depend on the permissions of the directories
30 occurring in the path to the file, as given in
31 ''pathname'', and on the permissions of directories and
32 files referred to by symbolic links encountered on the
33 way.
34
35
36 The check is done with the process's ''real'' uid and
37 gid, rather than with the effective ids as is done when
38 actually attempting an operation. This is to allow set-UID
39 programs to easily determine the invoking user's
40 authority.
41
42
43 Only access bits are checked, not the file type or contents.
44 Therefore, if a directory is found to be
45 execve__(2) call will
46 still fail.
47 !!RETURN VALUE
48
49 On success (all requested permissions granted), zero is
50 returned. On error (at least one bit in ''mode'' asked
51 for a permission that is denied, or some other error
52 occurred), -1 is returned, and ''errno'' is set
53 appropriately.
2 PerryLorier 54
1 perry 55 !!ERRORS
56
2 PerryLorier 57 ;[EACCES]: The requested access would be denied to the file or search permission is denied to one of the directories in ''pathname''.
58 ;[EROFS]: Write permission was requested for a file on a read-only filesystem.
59 ;[EFAULT]: ''pathname'' points outside your accessible address space.
60 ;[EINVAL]: ''mode'' was incorrectly specified.
61 ;[ENAMETOOLONG]: ''pathname'' is too long.
62 ;[ENOENT]: A directory component in ''pathname'' would have been accessible but does not exist or was a dangling symbolic link.
63 ;[ENOTDIR]: A component used as a directory in ''pathname'' is not, in fact, a directory.
64 ;[ENOMEM]: Insufficient kernel memory was available.
65 ;[ELOOP]: Too many symbolic links were encountered in resolving ''pathname''.
66 ;[EIO]: An I/O error occurred.
1 perry 67
68 !!RESTRICTIONS
69 __access__ returns an error if any of the access types in
70 the requested call fails, even if other types might be
71 successful.
72
73 __access__ may not work correctly on NFS file systems
74 with UID mapping enabled, because UID mapping is done on the
75 server and hidden from the client, which checks
76 permissions.
77
78 Using __access__ to check if a user is authorized to e.g.
79 open a file before actually doing so using open(2)
80 creates a security hole, because the user might exploit the
81 short time interval between checking and opening the file to
82 manipulate it.
2 PerryLorier 83
1 perry 84 !!CONFORMING TO
85 SVID, AT
86 !!SEE ALSO
87
2 PerryLorier 88 stat(2), open(2), chmod(2), chown(2), setuid(2), setgid(2)
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