Basic Linux Commands - Virginia Tech
[Pages:50]Warnings
Basic Linux Commands 1
First of all, these notes will cover only a small subset of the available commands and utilities, and will cover most of those in a shallow fashion.
Read the relevant material in Sobell!
If you want to follow along with the examples that follow, and you do, open a Linux terminal.
Second, most of the Linux commands have features that are enabled by using commandline switches; check the man pages for the commands for details!
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Getting Started
Basic Linux Commands 2
The Linux terminal (or command shell) allows you to enter commands and execute programs.
A terminal displays a prompt and a cursor indicating it's waiting for user input:
The prompt itself is configurable; precisely how depends on the particular type of shell you are running.
It is likely that by default you will run the bash shell.
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What's Running?
Basic Linux Commands 3
The ps command displays information about processes the shell is currently running:
We see that two processes are executing, bash and ps.
Moreover, we see that: - each is assigned a unique numeric identifier called a process ID or PID - each is associated with a terminal (TTY) named pts/0
Try executing ps a second time... you'll notice that the PID for bash is the same as before but the PID for ps has changed.
Why? (That's two questions.)
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More Information
Basic Linux Commands 4
Try running the process snapshot command: ps with the ?l (that's ell, not one) switch:
Don't worry about the meaning of all that just yet, but do notice that the results of the ps command were altered by the use of a "switch" on the command line.
In this case, the ?l switch means show detailed information (a long listing).
This is typical of Linux commands and many user programs.
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One way to find out more...
Basic Linux Commands 5
The man (manual) command can be used to obtain more information about Linux commands:
The man pages are often the first resort for discovering options. Try running man man...
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The Linux Documentation Project
Basic Linux Commands 6
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File System Basics
Basic Linux Commands 7
The file system is a set of data structures that organizes collections of files.
Files are grouped into directories (although directories are themselves files).
Here's one possible file system organization:
root
super-directory (parent)
sub-directory (child)
regular file
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File System Basics
Basic Linux Commands 8
For my CentOS 8 installation, here's what the top-level of my file system looks like:
bin -> usr/bin boot dev etc home lib -> usr/lib lib64 -> usr/lib64 media mnt opt proc root run sbin -> usr/sbin srv sys tmp usr var
many common utilities boot-related info and utilities info about various devices system-wide configuration files user directories shared binaries
access to removable devices mount points optional software (usually non-standard) information about processes home directory of the root user transient files for running processes system administration binaries data for system services
temp files for running processes user utilities user logs, etc.
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?2005-2020 WD McQuain
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