Bash command hashing

Reference: https://unix.stackexchange.com/questions/554785/why-does-shell-use-executable-in-usr-bin-and-not-in-usr-local-bin

Bash will hash commands: amazing, In other words, when any command is executed without naming its path, the shell starts searching for that command within the directories, which are listed in the path variable. When the Bash gets that command, it keeps the location in a hash table so that it can remember the location of the command. After that, Bash starts checking the table to find the location of the command instead of looking for the command again. It makes the command run faster. However, if the command is moved after recording its location in a table, the shell will not be able to find the command. In this case, a full search of the directories in the path is performed to get the command data.

The Filesystem Hierarchy Standard describes the filesystem conventions of a Linux system. In this standard, folders /lib, /usr/lib and /usr/local/lib are the default folders to store shared libraries. The /lib folder has libraries used during the boot time of the system but also used by programs in the /bin folder. Similarly, the/usr/lib folder has libraries used by programs in the /usr/bin folder. Finally, /usr/local/lib folder has libraries used by programs in /usr/local/bin folder. Therefore, we may first check these standard paths to find out if a specific shared library is installed on our system. (You never know when you will use this information when you learn it …)

Libraries are also cached. So, after clear the command cache. You must clear the ldconfig cache. That’s what we will not learn from the textbook!!!!!! When teaching Linux kernel, also search on stack overflow: https://stackoverflow.com/questions/17889799/libraries-in-usr-local-lib-not-found