1path_resolution(7) Miscellaneous Information Manual path_resolution(7)
2
6 path_resolution - how a pathname is resolved to a file
7
9 Some UNIX/Linux system calls have as parameter one or more filenames.
10 A filename (or pathname) is resolved as follows.
11 Step 1: start of the resolution process
13 If the pathname starts with the '/' character, the starting lookup di‐
14 rectory is the root directory of the calling process. A process inher‐
15 its its root directory from its parent. Usually this will be the root
16 directory of the file hierarchy. A process may get a different root
17 directory by use of the chroot(2) system call, or may temporarily use a
18 different root directory by using openat2(2) with the RESOLVE_IN_ROOT
19 flag set.
20 A process may get an entirely private mount namespace in case it—or one
22 of its ancestors—was started by an invocation of the clone(2) system
23 call that had the CLONE_NEWNS flag set. This handles the '/' part of
24 the pathname.
25 If the pathname does not start with the '/' character, the starting
27 lookup directory of the resolution process is the current working di‐
28 rectory of the process — or in the case of openat(2)-style system
29 calls, the dfd argument (or the current working directory if AT_FDCWD
30 is passed as the dfd argument). The current working directory is in‐
31 herited from the parent, and can be changed by use of the chdir(2) sys‐
32 tem call.
33 Pathnames starting with a '/' character are called absolute pathnames.
35 Pathnames not starting with a '/' are called relative pathnames.
36 Step 2: walk along the path
38 Set the current lookup directory to the starting lookup directory.
39 Now, for each nonfinal component of the pathname, where a component is
40 a substring delimited by '/' characters, this component is looked up in
41 the current lookup directory.
42 If the process does not have search permission on the current lookup
44 directory, an EACCES error is returned ("Permission denied").
45 If the component is not found, an ENOENT error is returned ("No such
47 file or directory").
48 If the component is found, but is neither a directory nor a symbolic
50 link, an ENOTDIR error is returned ("Not a directory").
51 If the component is found and is a directory, we set the current lookup
53 directory to that directory, and go to the next component.
54 If the component is found and is a symbolic link, we first resolve this
56 symbolic link (with the current lookup directory as starting lookup di‐
57 rectory). Upon error, that error is returned. If the result is not a
58 directory, an ENOTDIR error is returned. If the resolution of the sym‐
59 bolic link is successful and returns a directory, we set the current
60 lookup directory to that directory, and go to the next component. Note
61 that the resolution process here can involve recursion if the prefix
62 ('dirname') component of a pathname contains a filename that is a sym‐
63 bolic link that resolves to a directory (where the prefix component of
64 that directory may contain a symbolic link, and so on). In order to
65 protect the kernel against stack overflow, and also to protect against
66 denial of service, there are limits on the maximum recursion depth, and
67 on the maximum number of symbolic links followed. An ELOOP error is
68 returned when the maximum is