What does double slash // in `cd //` mean in Linux?

Question

I've entered a command cd // instead of cd / by mistake and instead of getting an error as I'd expect the shell (Bash) showed a prompt as if I'm in the // directory:-

<username>@<hostname>://$
<username>@<hostname>://$ pwd
//

Listing the content of the directory shows that it is the same as /.

So what exactly cd // do and what's the difference from cd /?

There's no difference. Try "//////////", it'll work as well. — Ernest Friedman-Hill, Dec 19 '13 at 20:17
"//////////" works, but I get a different prompt with a single '/'. — vitaut, Dec 19 '13 at 20:18
The bash builtin `pwd` command remembers the string you gave it (but normalizes it in some cases). `/bin/pwd` infers the full path from the location of your current directory, traversing `..` links as needed, and will print just `/`. — Keith Thompson, Dec 19 '13 at 20:23

Rahul Tripathi · Accepted Answer · 2013-12-19T20:23:23.297

62

Actually it means nothing and is ignored.

From the Bash FAQ E10::

E10) Why does 'cd //' leave $PWD as '//'?

POSIX.2, in its description of 'cd', says that three or more leading slashes may be replaced with a single slash when canonicalizing the current working directory.

This is, I presume, for historical compatibility. Certain versions of Unix, and early network file systems, used paths of the form //hostname/path to access 'path' on server 'hostname'.

Also the Unix standards states:

A pathname that begins with two successive slashes may be interpreted in an implementation-defined manner, although more than two leading slashes shall be treated as a single slash.

edited Dec 19 '13 at 20:23

answered Dec 19 '13 at 20:17

Rahul Tripathi

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**The `//` does not mean nothing**. It's defined by POSIX such that it may be _interpreted in an implementation-defined manner_, which means the system is free to do with it what it will. For example, on Cygwin, `cd //` followed by `ls` eventually returns `ls: reading directory '.': Permission denied`. whereas `cd /` followed by `ls` returns a listing of the root directory. (Cygwin uses a root of `//` to identify //hostname/path.) – roaima Aug 18 '22 at 12:54

score 21 · Answer 2 · edited Apr 13 '17 at 12:22

This answer on AskUbuntu confirms that they are the same directory. Further, it helpfully quotes from the POSIX Pathname Resolution specification:

A pathname consisting of a single slash shall resolve to the root directory of the process. A null pathname shall not be successfully resolved. A pathname that begins with two successive slashes may be interpreted in an implementation-defined manner, although more than two leading slashes shall be treated as a single slash.

What does double slash // in `cd //` mean in Linux?

2 Answers2

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