is this unix /var/blay/blah some kind of example convention?

Question

Whenever I see unix tutorials, I see them using:

/var/...

is var just a placeholder for an example?

Answer 1

No. /var is a directory. It tends to contains "variable" data - that is data that is going to tend to change and often not configuration files. (eg. /var/mail for mail storage, /var/vm for where virtual memory is stored)

For more information on how directories are laid out on Unix check out question 24523

Answer 2

No, /var is a directory in the filesystem. One of the directories often referred to that exists under that is /var/log where most of the system and many of the application logs are kept.

"foo", "bar", "baz" and the like are placeholders.

Answer 3

The top-level unix directory names are largely influenced by how these systems were configured decades ago. Here's a quick run-down of the more common ones:

• /bin/ - programs that are part of the "core" of the system, i.e. required at startup
• /boot/ - files requried during the boot process of the system (such as the kernel)
• /dev/ - device nodes (placeholder files representing devices such as disks)
• /etc/ - your configuration files
• /home/ - directories belonging to actual users
• /lib/ - shared librararies and other files that are part of the installed programs, but not directly runnable.
• /sbin/ - same as /bin, but should only be run by root.
• /tmp/ - temporary files (anyone can use this directory)
• /usr/ - files that aren't system-critical, but are part of the system.
• /var/ - files that change, but should be retained between boots

Traditionally, /usr was actually mounted as a network filesystem once the system was operational. So /bin and /sbin (which were stored on the local machine) only contained the stuff necessary to get that remote access up and running. /usr/ in turn contains elements of the "standard" directory tree, including /usr/bin/, /usr/sbin/, /usr/lib/, /usr/etc/, etc.

In the same way, /usr/local/ contained a set of programs, files, etc., that were "local" to a given installation, i.e. not part of the standard distribution. Again, expect to see /usr/local/bin/, /usr/local/lib/, etc. On a newly installed machine, those directories should be relatively empty, and it's a pretty safe place to install your own programs without creating any conflicts with the base system.

Traditionally, /tmp/ was erased upon boot, so stuff put there shoudn't need to stick around. /var/ on the other hand, contains a more permanant storage area. Things that end up under /var/ include database files, log files, and mail boxes.

If all the packages on your system are well-behaved, you should be able to put the entire system on read-only media (such as a CD), except have /var/ (and maybe /home/) be on a writable device, and /tmp/ be a ramdrive.