1PATH_RESOLUTION(7) Linux Programmer's Manual PATH_RESOLUTION(7)
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6 path_resolution - how a pathname is resolved to a file
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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 ancestors—
19 was started by an invocation of the clone(2) system call that had the
20 CLONE_NEWNS flag set.) This handles the '/' part of the pathname.
21 If the pathname does not start with the '/' character, the starting
23 lookup directory of the resolution process is the current working
24 directory of the process. (This is also inherited from the parent. It
25 can be changed by use of the chdir(2) system call.)
26 Pathnames starting with a '/' character are called absolute pathnames.
28 Pathnames not starting with a '/' are called relative pathnames.
29 Step 2: walk along the path
31 Set the current lookup directory to the starting lookup directory.
32 Now, for each nonfinal component of the pathname, where a component is
33 a substring delimited by '/' characters, this component is looked up in
34 the current lookup directory.
35 If the process does not have search permission on the current lookup
37 directory, an EACCES error is returned ("Permission denied").
38 If the component is not found, an ENOENT error is returned ("No such
40 file or directory").
41 If the component is found, but is neither a directory nor a symbolic
43 link, an ENOTDIR error is returned ("Not a directory").
44 If the component is found and is a directory, we set the current lookup
46 directory to that directory, and go to the next component.
47 If the component is found and is a symbolic link (symlink), we first
49 resolve this symbolic link (with the current lookup directory as start‐
50 ing lookup directory). Upon error, that error is returned. If the
51 result is not a directory, an ENOTDIR error is returned. If the reso‐
52 lution of the symlink is successful and returns a directory, we set the
53 current lookup directory to that directory, and go to the next compo‐
54 nent. Note that the resolution process here involves recursion. In
55 order to protect the kernel against stack overflow, and also to protect
56 against denial of service, there are limits on the maximum recursion
57 depth, and on the maximum number of symbolic links followed. An ELOOP
58 error is returned when the maximum is exceeded ("Too many levels of
59 symbolic links").
60 Step 3: find the final entry
62 The lookup of the final component of the pathname goes just like that
63 of all other components, as described in the previous step, with two
64 differences: (i) the final component need not be a directory (at least
65 as far as the path resolution process is concerned—it may have to be a
66 directory, or a nondirectory, because of the requirements of the spe‐
67 cific system call), and (ii) it is not necessarily an error if the com