why there is two identical bash?

Question

I have seen some bash scripts start with /user/bin/bash and others/bin/bash

I did a check-sum with cksum

2695035772 1392424 /usr/bin/bash
2695035772 1392424 /bin/bash

they look exactly the same, so what's the difference.Is it more appropriate to use one than one another in bash scripts?

These days, /bin and /usr/bin are the same directory (one a link), so bash is just the one file. — ubfan1, May 14 '22 at 19:46
Related: Why are /bin and /sbin now symlinks in Ubuntu 20.04? and usrmerge of {/bin, /sbin, /lib}: How is the system supposed to be? — steeldriver, May 14 '22 at 20:49

score 7 · Answer 1 · answered May 14 '22 at 19:55

7

/bin is linked to /usr/bin so the two are literally the same. Same goes for sbin. It is due to historical, compatibility reasons. bash predates Linux so to be more compatible we still use both.

$ ls -l  / | grep bin 
lrwxrwxrwx   1 root     root              7 apr  3 00:13 bin -> usr/bin
lrwxrwxrwx   1 root     root              8 apr  3 00:13 sbin -> usr/sbin

We are going towards /usr/bin/bash. Fedora is ahead of Debian/Ubuntu and OpenSUSE on this (those use /bin/bash).

answered May 14 '22 at 19:55

Rinzwind

299,756

Debian uses /bin symlink to /usr/bin too, for new installs (I think since buster). For upgraded installs, you must temporarily install usrmerge package, which does the conversion in post install hook. See https://wiki.debian.org/UsrMerge – Dalibor Filus May 15 '22 at 11:24

score 4 · Answer 2 · edited Aug 22 '23 at 09:15

4

As ubfan1 said in a comment, the /bin directory is now (not sure when this happened, but it's unimportant) simply a link to /usr/bin, so /bin/bash and /usr/bin/bash point to the exact same place in the system, thus the identical checksums.

edited Aug 22 '23 at 09:15

BeastOfCaerbannog

14,585

answered May 14 '22 at 19:55

Azzy

37

score 3 · Answer 3 · edited Aug 21 '23 at 18:19

There is only a single "bash" executable. The directory /bin is now replaced by a symbolic link to /usr/bin. Therefore, both /bin/bash and /usr/bin/bash are the same executable.

Historically, bash as a core utility used to be in /bin. Hard drives were small, so there was a need to keep the system partition small. Core binaries were collected in /bin, which resided on the hard drive from which the system booted. A directory /usr/bin was then designed to host other binaries, that eventually were present on a partition on another drive, mounted later in the boot process.

Storage is nowadays plenty, so there is a tendency to do away with the historical split between /bin and /usr/bin. Many distributions started to move any executable to /usr/bin instead, but, for compatibility reasons, still have a /bin, which really is only a symbolic link to /usr/bin. This way, the traditional shebang #!/bin/bash continues to work, although /bin my disappear completely in the future.

why there is two identical bash?

3 Answers3

Linked