Is there any executable file that is 100% going to be in /bin?

[Botspot]

No matter what OS, no matter if it has a GUI, no matter if it uses systemd or sysvinit, are there any executable files that are going to exist in 100% of linux releases?
Weird question, I know. The reason why I ask is because I need a foolproof way of detecting whether what CPU architecture a given OS is meant for 32-bit, 64-bit, armhf, x86, you name it. And the detection must be done automatically and silently using a bash script.
(I thought the easiest way to detect it would be to find an executable file and detect what CPU architecture it's meant for)

[jahboater]

No matter what OS, no matter if it has a GUI, no matter if it uses systemd or sysvinit, are there any executable files that are going to exist in 100% of linux releases?
Weird question, I know. The reason why I ask is because I need a foolproof way of detecting whether what CPU architecture a given OS is meant for 32-bit, 64-bit, armhf, x86, you name it. And the detection must be done automatically and silently using a bash script.
(I thought the easiest way to detect it would be to find an executable file and detect what CPU architecture it's meant for)

Do you mean like "file /bin/sh" ?
I think /bin/sh will always be there even if its a link to /bin/dash

[Botspot]

Do you mean like "file /bin/sh" ?
I think /bin/sh will always be there even if its a link to /bin/dash

That could probably work.
But I'd have to find a way to follow the symlink or else when I try to detect the mimetype it will look like this:

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$ file --mime-type -b /media/pi/pi-power-tools/bin/sh
inode/symlink

[DougieLawson]

You'll always have /sbin/init as that's the program that the kernel starts (unless you override it in /boot/cmdline.txt).

[Botspot]

You'll always have /sbin/init as that's the program that the kernel starts (unless you override it in /boot/cmdline.txt).

Another good answer. Too bad init can also be a symlink. Though again, I suppose the script could handle that and follow the symlink before getting the filetype.

[kerry_s]

why not just do /bin/bash
i figure if it's a bash script & there's no bash your screwed anyways. i've never come across a linux without a bash shell or i don't remember.

[DougieLawson]

If you're doing it in busybox then /bin/busybox must exist (unless you have some funky way of launching busybox).

[jahboater]

why not just do /bin/bash
i figure if it's a bash script & there's no bash your screwed anyways. i've never come across a linux without a bash shell or i don't remember.

POSIX mandates that /bin/sh must exist.

[DougieLawson]

POSIX mandates that /bin/sh must exist.

On RaspiOS that's a symlink to /bin/dash.

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pi@ulysses:/bin $ ls -la sh
lrwxrwxrwx 1 root root 4 Jun 20  2019 sh -> dash
pi@ulysses:/bin $ readlink /bin/sh
dash
pi@ulysses:/bin $

[DarkElvenAngel]

why not just do /bin/bash
i figure if it's a bash script & there's no bash your screwed anyways. i've never come across a linux without a bash shell or i don't remember.

Busybox based distributions don't have bash. Also if busybox is used as the init for a distribution then init is a script.

[trejan]

What are you trying to achieve by doing this anyway? The requirement it must work on everything is going to give you lots of weird edge cases to deal with like a multi arch install of Debian. Are you trying to write a system information script?

[DarkElvenAngel]

I agree there is going to be somewhere that doesn't put things in the same place or you have a 64 bit kernel and a 32 bit user land.

I was going to suggest parsing the uname output but then you might have trouble with that one too.

[cleverca22]

You'll always have /sbin/init as that's the program that the kernel starts (unless you override it in /boot/cmdline.txt).

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[root@amd-nixos:~]# ls -l /sbin
ls: cannot access '/sbin': No such file or directory

[root@amd-nixos:~]# ls -l /lib
ls: cannot access '/lib': No such file or directory

[root@amd-nixos:~]# 

not all distros conform to such rules!, parsing uname will likely be simpler, just "uname -m" i believe

[ejolson]

Do you mean like "file /bin/sh" ?
I think /bin/sh will always be there even if its a link to /bin/dash

That could probably work.
But I'd have to find a way to follow the symlink or else when I try to detect the mimetype it will look like this:

Code: Select all

$ file --mime-type -b /media/pi/pi-power-tools/bin/sh
inode/symlink

If you are going to use file to detect the mimetype, doesn't that imply that the file program is installed and working? If it is, then use file to check whether file itself is a 32-bit or 64-bit executable.

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$ file /usr/bin/file
/usr/bin/file: ELF 32-bit LSB executable, ARM, EABI5 version 1 (SYSV), dynamically linked, interpreter /lib/ld-linux-armhf.so.3, for GNU/Linux 3.2.0, BuildID[sha1]=7df606942d83740a79979415e18b9960f0344ff2, stripped

Of course that's in /usr/bin, so maybe not quite the answer you wanted.

[swampdog]

I usually start with 'uname' and work from there but to answer your question, I guess we need to find a native executable using minimum tools..

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#!/usr/bin/env sh

E="/bin/sh"
[ -f "$E" ] || exit 1
X=$(readlink "$E")
[ -z "$X" ] && X="$E"
X="$(which $X)"
$(which file) "$X" || exit 1

The above ought to work for other unix as well, BSD's etc that don't have things like /proc/version and /etc/(os-release|redhat-release) and so forth. For instance, the above 'readlink' could be simplified via "-m" option but the BSD's don't have it.