Lecture 1 - Linux Refresher

7/30/2019 Lecture 1 - Linux Refresher

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Linux RefresherFall 2013

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Topics

Linux Overview

Linux distributions

System overview

More detail: permissions, processes, package management,

services

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Linux Overview

Unix-like operating system

Free, open source software

Runs servers, desktops, phones, tablets, network equipment

and more.

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Linux Distributions

Packaging of applications around aLinux kernel

Different distributions havedifferent target audiences

Distribution lifecycles

Suse, Fedora, RedHat Enterprise,CentOS, Debian, Ubuntu, Mint,Gentoo, Arch

Quick Stat:

~ 94% ofthe worlds top 500supercomputers run some variant ofLinux (including the 10 fastest)

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Choosing a Distribution

Server/desktop/other

Existing infrastructure

Admin experience

Support contract

Release supported lifetime

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The Kernel

Computer program that manages

input/output requests from

software

Translates requests into data

processing instructions for thecentral processing unit and other

electronic components

Fundamental aspect of all modern

OSs

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http://localhost/var/www/apps/conversion/tmp/scratch_4//upload.wikimedia.org/wikipedia/commons/8/8f/Kernel_Layout.svg


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Users and Groups

Users and groups are stored in /etc/passwd and /etc/group

User passwords are stored in /etc/shadow

Each user name and group name is linked to a number

(UID/GID)

UID 0 = root

0-99 typically used for system/service accounts

root user = full access to everything on the system

sudo , su switch user

Don't use root user unless you have to!

Common commands:

useradd, usermod, userdel, passwd, chage, groupadd

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Linux Directory Structure

Filesystem Hierarchy Standard (FHS)

Shareable vs. Unshareable

Static vs. Variable

Common commands:

cd

ls

pwd

touch

rmdir

rm

cp

ln (hard and soft links)8


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File Permissions

Every file

Is owned by someone

Belongs to a group

Has certain access permissions for owner, group, and others

The long version of a file listing (ls -l) will display the file

permissions:

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-rwxrwxr-x 1 rvdheij rvdheij 5224 Dec 30 03:22 hello

-rw-rw-r-- 1 rvdheij rvdheij 221 Dec 30 03:59 hello.c

-rw-rw-r-- 1 rvdheij rvdheij 1514 Dec 30 03:59 hello.s

drwxrwxr-x 7 rvdheij rvdheij 1024 Dec 31 14:52 posixuft

Permissions

Owner

Group


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Changing File Permissions

Use the chmod command to change file permissions

The permissions are encoded as an octal number

Three roles: user (file owner), group, other (world)

Three permissions: read, write, execute

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chmod 755 file # Owner=rwx Group=r-x Other=r-x

chmod 500 file2 # Owner=r-x Group=--- Other=---

chmod 644 file3 # Owner=rw- Group=r-- Other=r--

chmod +x file # Add execute permission to file for all

chmod o-r file # Remove read permission for others

chmod a+w file # Add write permission for everyone
http://linux.com.hk/man/showman.cgi?manpath=/man/man1/chmod.1.inchttp://linux.com.hk/man/showman.cgi?manpath=/man/man1/chmod.1.inc


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Linux Device Handling

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Devices are the way linux talks to the world

Devices are special files in the /dev directory (try ls /dev)

/dev/hdb IDE hard drive

/dev/hdb1 Partition 1 on the IDE hard drive

/dev/mnda VM Minidisk

/dev/dda Channel Attached DASD

/dev/dda1 Partition 1 on DASD

/dev/null The null device (hole)

/dev/zero An endless stream of zeroes

/dev/mouse Link to mouse (not /390)


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Editors / Shell Scripting

Vim Three modes (Command/Insert/Extended)

Environment variables ( e.g. PATH)

Variables Direct assignment, prompt, positional

Exit status codes (success -> 0)

Conditional statements

Case statements

Looping

Displaying contents of files

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Backup and Recovery

System backups are important! (e.g. /etc, /home)

Tar utility

Cpio

Compression (e.g. Gzip)

Scheduling (Cron)

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Installing and Managing Software

YaST

RPMs

Many advantages:

Dependency checks

preinstalltion tasks

Conflicts

Unpacking

postinstallation

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Documentation

Most packages include man pages for documentation

More extensive than the --help flag on CLI

Stored in different 'sections'

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Documents

Lecture 1 - Linux Refresher