Directory – Managing Deep-Created Directories in Linux

directory

  1. In Windows, there is a certain limit on the number of characters in
    a path, which restricts how deep a directory can be created. I was
    wondering what the case is like in Linux?
  2. Do you have some suggestions on how to organize directories to
    achieve the same or close enough benefits (such as good for organization) of deep directory structures, with less potential trouble
    one may run into?

Best Answer

The actual limits can depend both on the filesystem you're using, and the kernel.

To find out the limits for a particular mount point, you can use getconf (ex. for / on my machine):

$ getconf  PATH_MAX /
4096
$ getconf  NAME_MAX /
255

PATH_MAX is the maximum total length, NAME_MAX if for the filename. The kernel limits are in include/linux/limits.h in the kernel source:

#define NAME_MAX         255    /* # chars in a file name */
#define PATH_MAX        4096    /* # chars in a path name including nul */

For a list of filesystem limits, see Comparison of file systems.

The filesystem limits dictate the maximum nesting level (if any) for directories and then length of file and directory names for that filesystem. The kernel limits dictate how long strings that refer to paths can be.
You can actually have a nesting structure that exceeds the PATH_MAX limit. But you won't be able to refer to it with a fully-qualified path from root. You should also expect strange software bugs if you use such deep structures, since a lot of code expects paths to fit within PATH_MAX buffers, and checking for ENAMETOOLONG errors (and correctly recovering from them) is probably not one of the best-tested code paths out there.

As for organization, just use whatever feels more natural. Keep hierarchies reasonable, avoid strange characters (and whitespace) if you want to be script-safe/friendly. Those limits are quite generous. If you ever get near PATH_MAX, it's probably time to reorganize things.

If you do want to test out how things behave in very lengthy paths, here's a fast way to generate huge paths:

#! /usr/bin/perl

my $kd = "a" x 255;
for my $i (1..64) {
  mkdir($kd); chdir($kd);
}

If you want a deep hierarchy, try with:

#! /usr/bin/perl

my $kd = "a";
for my $i (1..8192) {
  mkdir($kd); chdir($kd);
}

And you can get:

$ pwd | wc -c
16394

But ksh gets a bit confused:

$ cd ..
ksh: cd: ..: [File name too long]

bash does do the cd .., but the prompt is messed up, the directory name is not resolved - so pwd | wc -c is actually 16397 after that.

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