Introduction To Linux

By Owen Stampflee <owen@stampflee.com>

http://www.stampflee.com/vlug-intro2linux.pdf

1. File System Hierarchy
2. File Utilities
3. Text Utilities
4. Users & Groups
5. Networking
6. Backup Tools
7. Package Management
8. Compiling Software From Source
9. System Resource Management
10. Miscellaneous

File System Hierarchy

/bin - Core Applications

/boot - Contains Kernels and Boot loader Components

/dev - Device files

/etc - Global System Configuration Files

/home - User data files

/lib - Core Libraries

/mnt - Directories where secondary file systems and media are mounted.

/opt - Commercial software and sometimes KDE and Gnome.

/proc - Special kernel file system

/root - The super user's data files. Should remain nearly empty.

/sbin - Core Applications for the Super User.

/tmp - Temporary Files

File System Hierarchy Cont.

/usr

• bin - User Applications
• include - Include files
• lib - User Libraries
• local - Locally Compiled Applications, Libraries, Shared Files, Etc.
• sbin - Super User Applications
• share - Shared files including pixmaps, menus, documentation, and man pages.
• src - Source code for various applications.
• X11R6 - Applications, Libraries, Shared files packaged in XFree86.

/var - Various files data files.

• lock - Files that indicate if background processes (daemons) are running (or weren't stopped cleanly) 
• log - (IMPORTANT) Log files, if something goes wrong, this is where you look!
• run - Files that contain process identifiers used to stop daemons.
• spool - Spool files for mail, print, and other servers

File Utilities

ls options path - Lists Files.

• -l : Long view
• -h : Human Readable Sizes (only with -l)
• -a : List All files

cd options path - Change Directory

• Use just cd with no arguments to change to your home directory.

cp options source destination - Copy source file to destination file.

• -a : Archive, copies recursively preserving permissions.
• You can have multiple source files if the destination is a directory.

mv options source destination - Move (or rename) source file to destination file.

• -a is "on" by default.
• As with cp you can have multiple source files if the destination is a directory.

File Utilities Cont.

chmod options mode path - Changes the permissions the path to the specified mode.

• -R : Changes Permissions Recursively
• Mode is in the form of u=rwx,g=rwx,a=rwx.
• "u" is the owner of the file, "g" is the group of the file, and "a" is for anyone.
• "r" is for read permissions, "w" is for write, and "x" determines if the file is executable.

chown options user.group path - Changes the owner and group of a path to the specified user.group

• ".group" does not need to be specified if the you do not want change the group.
• If you don't want to change the user, just the group use chgrp instead.

File Utilities Cont.

du options path - summarizes disk usage

• -h : Human readable sizes
• -s : Summary

df options - Calculates disk usage on mounted partitions.

• -h : Human readable sizes.

find path options - Finds files in path that satisfy the options.

• -name : Name of the file. Use asterisks for a wild card.
• -type : Type of the file, "f" for normal files, "d" for directories, "l" for links.
• See man page for more options, there's lots of them!
• You can also use operators in the options such as -and, -or, and -not.

Text Utilities

cat file - Outputs the specified file to Standard Output (stdout).

head -n file - Outputs the first the n lines of the specified file to stdout. 

• If -n is omitted, outputs the first 10 lines.
• If no file is specified, Standard Input (stdin) is used instead.

tail -n file - Outputs the last the n lines of the specified file to stdout. 

• If -n is omitted, outputs the last 10 lines.
• If no file is specified, Standard Input (stdin) is used instead.

grep options pattern file - Outputs lines from the specified file that match the pattern. 

• -v : Outputs the lines that don't match the pattern.
• If no file is specified, Standard Input (stdin) is used instead.

Text Utilities Cont.

sed s:old:new:g file - Replaces all occurrences of "old" with "new"

• You can specify multiple expressions by using -e
• If no file is specified, Standard Input (stdin) is used instead.

Pipes

A pipe "|" will take the output of the first command and pass it to the second on standard input.

Redirectors

The ">" redirector, will write the output of the command before it and write it to the file specified after it.

The "<" redirector, will take the contents of the file after it and write as standard input to the application run before it.

Users & Groups

useradd options user - Creates a new user.

• -g : Comma separated groups the user is a member of.
• -M : Create the user's home directory if doesn't exist.
• -s : The user's shell. (Use /bin/false for users you wish to restrict from having shell access).

usermod options user - Modifies user account

• Same options as useradd.

userdel options user - Deletes user account.

• -r : Remove user's home directory.

passwd user - Changes the password of the specified user. 

• If no user is specified, will change the password of the current user.

Users & Groups Cont.

groupadd group - Creates a group.

groupmod options group - Modifies a group.

• -n : Rename group

groupdel group - Deletes the specified group.

sudo command - Runs command as root.

• /etc/sudoers  should have a line which contains the following:

"%wheel  ALL=(ALL)       ALL". This can be achieved but uncommenting

that line in the standard /etc/sudoers.

• Then add users you wish to have access to sudo to the "wheel" group.

Networking

ifconfig interface - Shows information about the specified interface, if no interface is specified, shows information about all active interface.

ifconfig interface ip_addr up - Configures the specified interface with ip_addr.

ifconfig interface down - Takes down interface. Akin to unplugging the cable.

route - Show routing table.

• -n : Don't look up names of IP addresses in routing table.

route add default gw ip_addr - Makes the specified ip_addr one of the default gateways.

route del default gw ip_addr - Removes the specified default gateway.

ping host - Test network connection to see if you can "talk to" the specified host.

Networking Cont.

/etc/resolv.conf is used by Glibc to determine how to look up Internet names. It contains the domain name to lookup as well as the name servers.

Sample /etc/resolv.conf:

domain lan.stampflee.com

nameserver 192.168.0.254

search lan.stampflee.com

/etc/hosts defines names of hosts and their IP addresses. Instead of looking up the name of the specified host with a name server, the IP address defined in /etc/hosts is used.

Example /etc/hosts:

127.0.0.1   localhost.localdomain localhost

192.168.0.1 	tsunami.lan.stampflee.com tsunami

192.168.0.2 	whitefusion.lan.stampflee.com whitefusion

192.168.0.254 	fred.lan.stampflee.com fred

Networking

dhcpcd interface - Try to fetch a DHCP lease.

dhcpcd -k interface - Kill dhcpcd and release your DHCP lease.

dhcpcd is not the only DHCP client that exists, if your system doesn't have it, pump and dhclient are popular alternatives.

netstat options - Show various network statistics.

• -l : List ports where a process is listening.
• -t : Only show information about TCP connections and ports.
• -u : Only show information about ICMP connections and ports.

Backup Tools

tar jxvf mytarball.tar.bz2 - Extract files from mytarball.tar.bz2

tar zxvf mytarball.tar.gz - Extract files from mytarball.tar.gz

• -z : Use gzip compression
• -j : Use bzip2 compression
• -x : Extract
• -v : Verbose
• -f : Use file

Gzip compression is used for tarballs with the extensions .tar.gz, .tgz, and .tar.Z. Bzip2 compression which is slightly better but requires more CPU is used in tarballs with the extensions .tar.bz2 and .tbz2.

tar jcvf mytarball.tar.bz2 my_files - Creates a tarball mytarball.tar.bz2 with the specified files.

Backup Tools Cont.

gzip file - Will compress file using gzip compression and will rename "file" to "file.gz"

gunzip file.gz - Will uncompress file compressed using gzip compression and will rename "file.gz" to "file"

bzip2 file - Will compress file using bzip2 compression and will rename "file" to "file.bz2"

bunzip2 file.bz2 - Will uncompress file compressed using bzip2 compression and will rename "file.bz2" to "file"

rsync options user@host:remote_directory local_directory - Will sync the remote_directory on the remote host with the local_directory.

• -a : Archive, Recursive.
• -v : Verbose
• -z : Compress
• -e : Remote shell (should use ssh)

Package Management

Using RPM

To install or upgrade a package:

	rpm -Uvh package-1.0.i386.rpm

To remove a package:

	rpm -e package-1.0

To determine what version of a package you have installed:

	rpm -qa | grep package_name

To determine what package a file "belongs" to:

	rpm -qf file

Package Management Cont.

Using Apt

To update your package lists:

	apt-get update

To install all updated packages:

	apt-get dist-upgrade

To install a package:

	apt-get install package

To upgrade a package:

	apt-get upgrade package

To then remove that package (and all packages that depend on it):

	apt-get remove package

To search for a package:

	apt-cache search search_string

Compiling Software From Source

Compiling an Application:

1. Download the source.
2. Untar the source.
3. cd into the source directory.
4. Read the INSTALL, README, and any other files that look they contain instructions. (We'll assume this is autoconf based build process)
5. Run ./configure, ./configure --help will typically describe the many  many options you can set.
6. If there are no errors run make
7. If there are still no errors, run sudo make install (assuming you've setup sudo :)
8. Run you application! If it doesn't seem to be available, check your $PATH.

Compiling a single source file:

gcc -o myexecutable myfile.c - Compiles myfile.c naming the executable, myexecutable. Use g++ for C++ source files.

System Resource Management

uptime - Shows the computer uptime, but more importantly shows your load average.

free - Shows memory usage.

• -h : Human Readable.

ps options - Process List

• RTFM, it's big! Most common options are "-ef" and "aux"

kill -signal pids - Sends signal to specified PIDs

• SIGHUP used if no signal specified.
• Popular signals: SIGHUP, SIGKILL, SIGUSR1, SIGUSR2

killall -signal processes - Sends specified signal to specified processes.

• SIGHUP used if no signal specified.

System Resource Management

top - Show vital system information including uptime, load average, CPU & memory usage as well as a sorted process list.

• "M" : Sort by Resident Memory Usage
• "P" : Sort by CPU Usage
• "k" : Kill PID.

xkill - Run and click on the X application that doesn't want to die. Right click if you change your mind about wanting to terminate an application.

nice priority command - Runs a program with modified scheduling priority.

• -20 is the highest priority (real time) and 19 is lowest priority. 
• Only root can set a priority higher than 0.

renice priority options - Alters scheduling priority

• -p pid ... : Alter priority for specified PIDs.
• -u user : Alter all processes owned by the specified users.

Miscellaneous

Environment Variables:

printenv - Prints all environment variables.

echo $ENVAR - Prints specified the specified environment variable.

export ENVAR="foo" - sets $ENVAR to "foo".

Getting Help:

command --help; command -h - Will summarize basic options for the command. This is application dependent and doesn't always work. More detailed help can be found in the man/info pages.

man arguments - Manual Tool

• A single argument will look up the given manpage.
• -k string : Find all entries that contain string.

info arguments - Manual Tool

• A single argument will look up the given info page.
• --apropos=subject : Find all entries that contain string.

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Introduction To Linux - By Owen Stampflee <owen@stampflee.com>

http://www.stampflee.com/vlug-intro2linux.pdf