[Computer System] Linux /bin, /sbin/, /usr/bin, /usr/sbin

/bin: 
  This directory contains executable programs which are needed in single user mode and for all users.

/sbin: 

  Like /bin, this directory holds commands needed to boot the system such as init, ip, mount, but those commands are not frequently executed by normal users.

/usr/bin:

  This is the primary directory for executable programs and for all users.

/usr/sbin:

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

/usr/local:
  Neither of the above. Please 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

Reference: 

1. Filesystem Hierarchy Standard
2. Single User Mode
3. Ubuntu Explaination