Jobs, Man Pages, & Links

Whenever you run a command in a shell, any programs that it starts up are added to a “job”. You can do various things with these jobs, of which we’ll describe a few here.

Job Control (jobs, fg, bg)

It’s very common to want to run more than one program at the same time, or to temporarily stop running a program and resume it later. This section will teach you how to do that.

The job you are currently running and interacting with is known as the foreground job. Any other job you are running is known as a background job.

# list all jobs
$ jobs
[1]-  Running                 sleep 100 &
[2]+  Stopped                 vim

# start a job in the background (include '&' at end of line)
$ sleep 100 &
[1] 14884

# stop the current program and return to the terminal
$ vim
# (pressed ^Z while vim was running)
[2]+  Stopped                 vim

# bring a backgrounded (stopped or running) program into the
# foreground (takes control of the terminal)
$ jobs
[1]-  Running                 sleep 100 &
[2]+  Stopped                 vim
$ fg 1
sleep 100
# note: if the job has a '+' next to it, you can omit the job number

# start a stopped process, but put it in the background
$ jobs
[1]+  Stopped                 sleep 100
[2]-  Stopped                 vim
$ bg
[1]+ sleep 100 &
# control returns to terminal

Exiting from a REPL (^D)

If you’re working in python, coin, bash or any other program that repeatedly gets input from you while it’s running, you can almost always make the program exit by pressing ^D (or end of file, commonly abbreviated EOF).

These types of programs are called REPLs (read-eval-print-loop). They do exactly what their name says: read input from a user, evaluate it in some way, print the results of evaluating, and repeat the process. They stop when there is no more input, which you can signal by pressing ^D.

Quitting a Program (^C)

To ask a program to stop running, type ^C. (This may not always make the program quit immediately, but will in the majority of cases.)

Killing a Program (kill, ps)

Some programs can ignore the ^C signal. If this is the case, you have to hard quit the program using the kill command. kill has two forms:

$ kill -9 %<job number>
# OR
$ kill -9 <process id>

You’ve already seen how to get the job numbers with jobs. To get process IDs, you can run

$ ps u

Manual Pages (man)

There will come a time when you’re not sure how to do something on a terminal. In those cases, you’ll want to get help on how to do it. Thankfully, there are several useful resources to provide you with help.

man (short for “manual”) is one of the most commonly used help resources. You can type

$ man <command>

to get information on what a command does and what options you can give it.

  • You can search through a man page by typing /thing_i_want_to_find (note the slash at the beginning)
  • Advance from one match to the next by pressing n
  • Exit out of man by pressing q.

The --help flag

Most (not all) commands have a --help or -h option that will print out a message about how to use it. This message is generally shorter and easier to read through than the man page.


You can also use Google to look for answers to questions that are not as easily answered by man. StackOverflow tends to be a very good resource to answer questions. It’s important to be careful with Googling, since some answers are wrong or overly complicated.

A symbolic link is a special kind of file that contains a reference to another file. You can use symbolic links to create short names to refer to files in another directory. For example,

$ ln -s GoogleDrive/Documents/Programming/ programming

~/links$ ls -l programming
lrwxr-xr-x 1 jake staff 45 Oct 17 19:15 programming -> GoogleDrive/Documents/Programming/

~/links$ ls

ln has a lot of options and forms, but when you just want to make a file link to another file or directory, the syntax is

$ ln -s <to_file> <from_file>

This can be hard to remember. I personally find it easy to think about it in terms of the “arrow” that effectively gets drawn by linking one file to another. When using ls -l, the direction of this arrow is forward (->), but when using the ln -s command to create links, the arrow points backwards.

#              <----
$ ln -s <to_file> <from_file>
$ ls -l <from_file>
...omitted... <from_file> -> <to_file>
Copyright © 2014, Great Practical Ideas in Computer Science.