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Chapter 1. Sessions and Jobs

Table of Contents

  • Sessions
  • Variables (local vs environment)
  • Job control (process (fg) vs daemon (bg))
  • Signals

What is Bash

  • String-based command language.
  • Each command is delimited by whitespace.

What can you do with bash

  • Start, stop, and kill jobs.
  • Run jobs in foreground and background.

Sessions

Every time you login to your machine, open a new terminal window or tab, it will begin a new terminal session. That session will end when you log out or close the terminal.

These files are sourced (or run) in this order.

# Load system-wide profile.
source /etc/profile

# Load user setting profile.
source ~/.bash_profile

Sidenote:

  • /etc/profile is where you should specify system-wide startup commands for all users.
  • ~/.bash_profile is where you should define your aliases.

Variables

Why this doesn't work.

LOL = lol

Local variables

LOL=lol
printenvs
printenvs | grep LOL

Environment variables

export LOL=lol
printenvs
printenvs | grep LOL

Persisting and sourcing environment variables

echo "export LOL=lol" >> ~/.bashrc
source ~/.bashrc

Job Control

List all processes run by user.

$ ps u

List all basic and elevated processes by user.

$ ps au

Example commands

# Run sleep in foreground.
sleep 1000

# Run sleep in background.
sleep 2000 &

# Send interrupt signal (2 SIGINT)
$ ctrl-c

# Send suspend signal (17 SIGSTP)
$ ctrl-z

# Job control
$ jobs

# run suspended job in foreground (default is pop last stack)
$ fg
$ fg 1

# run suspended job in background (default is pop last stack)
$ bg
$ bg 1

Signals

Send a signal to a process. SIGTERM (least dangerous) is sent by default.

kill -9 <process-id>
kill -SIGKILL <process-id>

# Send SIGTERM.
killall sleep

# Send SIGKILL.
killall -9 sleep
killall -SIGKILL sleep

List of common signals

2 SIGINT
Interrupt signal. This signal is given to processes to interrupt them.
Programs can process this signal and act upon it.
You can also issue this signal directly by typing Ctrl-c in the terminal window where the program is running.

15 SIGTERM (DEFAULT)
Termination signal. This signal is given to processes to terminate them.
Again, programs can process this signal and act upon it.
This is the default signal sent by the kill command if no signal is specified.

9 SIGKILL
Kill signal. This signal causes the immediate termination of the process by the Linux kernel.
Programs cannot listen for this signal.

17 SIGSTOP
Stop signal. Suspends the current running process.