Differences between /bin, /sbin, /usr/bin, /usr/sbin, /usr/local/bin, /usr/local/sbin

Please refer to the Filesystem Hierarchy Standard (FHS) for Linux for this.

• /bin : For binaries usable before the /usr partition is mounted. This is used for trivial binaries used in the very early boot stage or ones that you need to have available in booting single-user mode. Think of binaries like cat, ls, etc.

• /sbin : Same, but for binaries with superuser (root) privileges required.

• /usr/bin : Same as first, but for general system-wide binaries.

• /usr/sbin : Same as above, but for binaries with superuser (root) privileges required.

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if I'm writing my own scripts, where should I add these?

None of the above. You should use /usr/local/bin or /usr/local/sbin for system-wide available scripts. The local path means it's not managed by the system packages (this is an error for Debian/Ubuntu packages).

For user-scoped scripts, use ~/bin (a personal bin folder in your home directory).

The FHS says for /usr/local:

Tertiary hierarchy for local data, specific to this host. Typically has further subdirectories, e.g., bin/, lib/, share/.

I had a similar question myself a year+ ago: Best directory to place my bash scripts?

System directories for binaries

man hier (hierarchy) lists all the directories. To get the ones just for binaries use:

$ man hier | grep -E 'bin$|sbin$|^.{7}(/bin)|^.{7}(/sbin)' -A2

       /bin   This directory contains executable programs which are needed in single user
              mode and to bring the system up or repair it.

--
       /sbin  Like  /bin,  this  directory  holds commands needed to boot the system, but
              which are usually not executed by normal users.

--
       /usr/X11R6/bin
              Binaries  which  belong  to the X-Window system; often, there is a symbolic
              link from the more traditional /usr/bin/X11 to here.
--
       /usr/bin
              This  is the primary directory for executable programs.  Most programs exe‐
              cuted by normal users which are not needed for booting or for repairing the
--
       /usr/local/bin
              Binaries for programs local to the site.

--
       /usr/local/sbin
              Locally installed programs for system administration.

--
       /usr/sbin
              This directory contains program binaries for  system  administration  which
              are  not  essential  for the boot process, for mounting /usr, or for system

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Where to put your own scripts?

For all users to access your scripts you can put them in /usr/local/bin. Keep in mind you need sudo access to add / change files here. See: Is there a standard place for placing custom Linux scripts?

For your own user ID scripts put them in /home/YOUR_NAME/bin. Keep in mind you have to create this directory first and relaunch the terminal to get the path automatically setup by ~/.profile. See: How to add /home/username/bin to $PATH?

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What I know I don't know

I'm contemplating taking some of my more complex bash scripts in Ask Ubuntu and setting them up with install scripts on github. Here are few examples:

• Automatically adjust display brightness based on sunrise and sunset
• A timer to set up different alarms simultaneosly
• Application that will lock screen after a set amount of time for Ubuntu
• Code version control between local files and AU answers

I think the scripts should be installed in /usr/bin which is in the $PATH, but I'm not sure on the appropriate place yet.