1PATH_RESOLUTION(7) Linux Programmer's Manual PATH_RESOLUTION(7)
2
6 Unix/Linux path resolution - find the file referred to by a filename
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
14 directory is the root directory of the calling process. (A process
15 inherits its root directory from its parent. Usually this will be the
16 root directory of the file hierarchy. A process may get a different
17 root directory by use of the chroot(2) system call. A process may get
18 an entirely private mount namespace in case it — or one of its ances‐
19 tors — was started by an invocation of the clone(2) system call that
20 had the CLONE_NEWNS flag set.) This handles the '/' part of the path‐
21 name.
22 If the pathname does not start with the '/' character, the starting
24 lookup directory of the resolution process is the current working
25 directory of the process. (This is also inherited from the parent. It
26 can be changed by use of the chdir(2) system call.)
27 Pathnames starting with a '/' character are called absolute pathnames.
29 Pathnames not starting with a '/' are called relative pathnames.
30 Step 2: Walk along the path
32 Set the current lookup directory to the starting lookup directory.
33 Now, for each non-final component of the pathname, where a component is
34 a substring delimited by '/' characters, this component is looked up in
35 the current lookup directory.
36 If the process does not have search permission on the current lookup
38 directory, an EACCES error is returned ("Permission denied").
39 If the component is not found, an ENOENT error is returned ("No such
41 file or directory").
42 If the component is found, but is neither a directory nor a symbolic
44 link, an ENOTDIR error is returned ("Not a directory").
45 If the component is found and is a directory, we set the current lookup
47 directory to that directory, and go to the next component.
48 If the component is found and is a symbolic link (symlink), we first
50 resolve this symbolic link (with the current lookup directory as start‐
51 ing lookup directory). Upon error, that error is returned. If the
52 result is not a directory, an ENOTDIR error is returned. If the reso‐
53 lution of the symlink is successful and returns a directory, we set the
54 current lookup directory to that directory, and go to the next compo‐
55 nent. Note that the resolution process here involves recursion. In
56 order to protect the kernel against stack overflow, and also to protect
57 against denial of service, there are limits on the maximum recursion
58 depth, and on the maximum number of symbolic links followed. An ELOOP
59 error is returned when the maximum is exceeded ("Too many levels of
60 symbolic links").
61 Step 3: Find the final entry
63 The lookup of the final component of the pathname goes just like that
64 of all other components, as described in the previous step, with two
65 differences: (i) the final component need not be a directory (at least
66 as far as the path resolution process is concerned — it may have to be
67 a directory, or a non-directory, because of the requirements of the
68 specific system call), and (ii) it