The document provides a comprehensive overview of Linux server administration, detailing tasks such as system monitoring, user and group management, filesystem management, software installation, and networking. Key components discussed include booting processes, runlevels, scheduling with cron, as well as configuring and managing various server services like Samba for file sharing, FTP for file transfer, and Apache for web serving. Additionally, it covers user security, privileges, and the organization of configuration files critical for system administration.

1. Linux Server
Administration
Padam Banthia Roshan Gulgulia

2. Systems Administration
O Administering the system?
O Keep the system up in a consistent state
O Monitor performance
O Babysit users, make changes on their behalf
O Install, configure, upgrade, maintain
O Backup, restore, disaster recovery

3. Sysadmins
O System administration handled by various
people
O Full time dedicated sysadmins on site
O Remote services
O Generic ‘IT’ personnel
O That user that seems to know what they’re
doing
O Can be a skill set central to a career path, or
a means to an end

4. Privilege Hierarchy
O Want to divide system privilege by account
O First step is file level permissions
O Default permissions limit end users in what
configuration files they can read and which
programs they can run
O Next level is within system programs
O Limit certain functions to only users with
‘elevated’ privileges

5. The Superuser
O By default, one account has elevated
privileges to issue any command, access
any file, and perform every function
O Superuser, a.k.a. root
O Technically, can change to anything – but
don’t
O User and group number 0

6. System Operation
O Booting the system
O Runlevels
O Modes
O Shutting down the system

7. Booting the System
O Power on, POST, hardware initialization
O Boot device selected by BIOS/user
interaction
O Master boot record of boot device read
O Initializes the bootloader
O lilo (LInux LOader)
O grub (GRand Unified Bootloader)

8. Booting, cont
O Boot loader selects and loads an OS kernel
O Kernel stored as an compiled image file
O Kernel loads modules for hardware and
software functions
O Interrupts, device management, memory
management, paging
O Last thing kernel does is call init

9. init
O First non-kernel code loaded
O Process number 1
O Acts as parent to all other processes on
system
O Handles starting services and programs
O Based on runlevel, runs the appropriate
scripts

10. Runlevels
O A set of defined system states that init can
bring the system into (varies on distro)
O 0: Halt/shutdown
O 1: Single user mode
O 2: Multiuser mode
O 3: Multiuser mode with networking
O 4: Not used
O 5: Multiuser mode with networking and GUI
O 6: Reboot

11. Runlevels, cont
O On boot, init checks /etc/inittab to see what
runlevel to bring system to
O To change runlevel after boot
O telinit runlevel
O shutdown/halt/reboot
O Any time the runlevel changes, init consults
a set of scripts to determine what to
stop/start

12. Scripts
O Init works with run command (rc) scripts
O Found in /etc/rc.d
O All scripts housed in /etc/rc.d/init.d
O Each script takes a parameter for changing
operation (start/stop/halt/reboot)
O Each runlevel has it’s own directory
O /etc/rc.d/rcN.d

13. Single User Mode
O Runlevel 1
O Console only – no terminals
O Very minimal environment
O Some filesystems might not be mounted
O Maintenance of filesystems
O Fixing configuration errors
O Disaster recovery

14. Multiuser Mode
O Runlevels 2-5
O Runlevel 2 allows terminal logins
O Runlevel 3 allows remote terminal logins
O Runlevel 5 enable X11 graphical
environment
O Runlevels 3 and 5 are the most common
levels for day-to-day operations

15. Shutting Down the System
O Syntax:
shutdown [options] time [message]
O Time: XX:XX or +X or NOW
O -k: don’t really shutdown, just send message
O -r: reboot
O -h: halt
O -c: cancel a shutdown
O halt: calls shutdown –h
O reboot: calls shutdown -r

16. Scheduling
O Linux systems uses the Cron system for time-
based job scheduling
O Allows users to schedule jobs to run
O Allows sysadmins to run jobs and batch
processes
O Different distros implement the structures
differently
O Most use /etc/crontab as primary set of
instructions
O Sometimes other files are used, like
/var/spool/cron/*

17. crontab
O Each line schedules a job
O Syntax:
* * * * * command
O First field is minutes (0-59)
O Second field is hours (0-23)
O Third is day of the month (1-31)
O Fourth is month of year (1-12)
O Fifth is day of week (0-6, starting with Sun)

18. Filesystem Management
O A Linux installation can be comprised of
many different filesystems
O Each filesystem (except for swap) is
connected to the filesystem hierarchy at a
specific point in the tree
O This is referred to as the mount point
O A sysadmin uses mount, umount and
/etc/fstab to manage these mounts

19. mount
O Syntax (most commonly):
mount –t type device directory
O Associates a device (partition, CD-ROM, etc)
formatted with a particular type of
filesystem with a specified directory in the
hierarchy
O Requires root privileges to mount in most
cases
O mount with no arguments displays list of
mounted filesystems

20. umount
O Syntax:
umount directory | device
O Removes that association
O Cannot umount if device is still being
accessed (i.e. open files)
O Again, most likely requires root privileges

21. fstab
O For filesystems that should be mounted on
boot every time, put them in /etc/fstab
O Basically a tab delimited file that contains
the command line parameters you’d give to
mount
O Device
O Mount point (directory)
O FS type
O Options (Readonly, attributes, etc)

22. Creating New Filesystems
O First use fdisk device to create a
partition
O Similar in function to old fdisk from DOS
O Use ? to display commands, p to display
partition info
O Once partition created, must be formatted
O mkfs –t type filesystem
O Once formatted, you can mount it

23. Monitoring Disk Usage
O du – disk usage on files and directories
O df – reports filesystem utilization
O lsof – list open file handles
O quota – configure and display user quotas
O quotactl
O quotacheck
O quotaon
O edquota

24. Installing Software
O The open source movement has provided an
enormous volume of freely available
programs
O Two primary methods of installing programs
O By source
O By package manager

25. Installing by Source
O Download source code
O Usually comes in a compressed tar archive
(.tar.gz or similar)
O Extract source code
O Configure the installation (usually
./configure)
O Then compile (make)
O Then copy into filesystem (make install)

26. Package Managers
O There are a wide variety of package
managers available for different Linux
distributions
O In turn, there are several different types of
packages available for each of these
managers
O Packages are an archived version of the
source code
O Often tailored to a specific architecture or
distribution

27. RPM
O Red Hat Package Manager
O Package format and manager created by
Red Hat developers
O Used widely by Red Hat, Red Hat-based
distros, and many others
O System maintains a local RPM database to
maintain consistency and track installs

28. RPM, cont
O Many different utilities for managing RPMs
O rpm: command line package manager for
installing/removing/configuring packages
O up2date: command line package manager
that fetches packages from internet and
resolves dependencies
O yum, yast: similar to up2date
O Many GUI frontends available to these
utilities

29. User Administration
O User configuration stored in /etc/passwd
O File got it’s name because it originally
contained passwords as well
O Security problem – too many processes need
to read passwd
O A shadow file used now instead (more in a
sec)
O Each line contains info for one user

30. passwd
jsmith:x:1001:1001:Joe Smith,Rm27,(234)555-8910,(234)555-
0044,email:/home/jsmith:/bin/bash
O First field is username
O Second was password – now a dummy char
O Third is userid (uid)
O Fourth is groupid (gid)
O Fifth is GECOS field
O Full name, contact info
O Gen. Elec. Comprehensive OS
O Sixth is user’s home directory
O Seventh is user’s default shell

31. passwd, cont
O Originally passwd contained a user’s
password information
O How it works
O User picks a password
O A random number is generated (called the
salt)
O The salt and the password is passed into a
hash function (a one-way cryptographic
algorithm)
O The salt and result are stored in ASCII

32. passwd, cont
O Problem – user-level programs need to read
passwd
O Get user name, location
O Home directory, shell
O So passwd was world readable
O So anyone on system could see a user’s
salted hash
O It’s encrypted – what’s the big deal???

33. Adding Users
O If you really wanted to, edit /etc/passwd
by hand
O Some distributions have graphical or
simplified ways to add users
O Most widely available however is command
line utility useradd

34. Adding Users, cont
O Syntax:
useradd [options] [-g group] [-
d home]
[-s shell] username
O -g to define user’s initial group
O -d to define user’s home directory
O -s to define user’s default shell
O Other options for expiration, using defaults,
etc

35. Deleting Users
O Again, could just hack /etc/passwd
O More elegant:
O Syntax: userdel [-r] username
O -r to delete home directory and it’s contents

36. Modifying Users
O Syntax: usermod [options]
username
O Options are pretty much identical to those of
useradd
O Also, -l to change the user’s login name
O And –G to list additional groups to add user
to

37. Group Management
O Group info housed in /etc/group
O Similar to user management
O groupadd
O groupdel
O groupmod

38. Daemons as Users
O For the most part, Linux daemons (services)
each run as a unique user account
O Provides additional security by segregating
processes and files
O Running daemons as root usually a bad idea
O Accounts usually created automatically and
assigned passwords
O Usually disabled from logging into system

39. Networking
O Linux is a powerful networking operating
system
O Much of it developed in tandem with the
Internet
O Ability to work as a client, server, or network
device
O Proxies, firewalls, routers, bridges, etc

40. Networking, cont
O Overall networking usually governed by
/etc/rc.d/init.d/network
O Invoked in runlevels 3 and 5 usually
O Network device/interface configurations in
either /etc/sysconfig/networking
or in /etc/sysconfig/network-
scripts
O Can either edit manually, or use utilities to
manage

41. ifconfig
O Displays or alters network device configs
O Syntax:
ifconfig interface
[options]
O With no options, shows interface’s config
O If interface omitted as well, show all configs
O Options include flags, IP address, subnet
mask, etc

42. hostname
O Used to set/display the computer’s network
name
O Depending on what protocols your network
uses, may also need to look at
O domainname
O dnsdomainname
O Especially important for Internet-accessible
systems
O Can be defined in /etc/sysconfig/network

43. Servers
O Samba Server
O FTP Server
O Web Server

44. What is Samba Server ?
O Samba is an Open Source Suite, that provides
seamless file and print services to SMB/CIFS
clients.
O Samba is freely available. With Samba, you
can share a Linux files system with Windows
and vice versa.
O You can also share printers connected to
either Linux or a system with Windows.
O Samba enables a Linux or Unix server to
function as a file server for client PCs running
Windows software.

45. Samba Server
O What is SMB?
O SMB stands for – Server Message Block.
O It is a protocol by which a lot of PC-related
machines share files and printers and other
information such as lists of available files and
printers.
O Operating systems that support this natively
include Windows, OS/2, and Linux. What is
CIFS?
O CIFS – Common Internet File System is a
protocol that is basically an updated SMB.

46. Samba Server

47. Samba Server Installation
O Step 1: Install the vsftpd package:
O [root@localhost Desktop] # yum install
vsftpd
O Step 2: Configure the software:
O [root@localhost Desktop] # vim
/etc/vsftpd/vsftpd.conf
O Step 3: Starting the service:
O [root@localhost Desktop] # systemctl start
smb
O The service of Samba Web Server is started.

48. FTP Server
O FTP (File Transfer Protocol) is the simplest and most
secure way to exchange files over the Internet.
O Transferring files from a client computer to a server
computer is called "uploading" and transferring from
a server to a client is "downloading".
O To access an FTP server, users must be able to
connect to the Internet or an intranet (via a modem
or local area network) with an FTP client program.
O FTP doesn’t not really move, it copies files from one
computer to another
O FTP is the file transfer protocol in the Internet's
TCP/IP protocol suite’s Application Layer.

49. FTP Client
O Some commonly used FTP clients include the
following:
O FileZilla- a popular FTP client that is freely
available for Windows, Macintosh, and Linux users
Available as a free download from the Internet.
O Fire FTP- a plug-in for the popular Firefox web
browser that can be used just like a standalone
FTP program Installed through the FireFox
browser.
O Dreamweaver- page layout/design program,
which include FTP access as one of its many
features Available for purchase from Adobe

50. FTP Features
O The FTP protocol is used for transferring one file at a
time, in either direction, between the client machine
(the one which initiated the connection, i.e. the
calling machine) and the server machine (which
provided the FTP service, i.e. the called machine).
O The FTP protocol can also perform other actions,
such as creating and deleting directories (only if they
are empty), listing files, deleting and renaming files,
etc.
O FTP allows files to have ownership and access
restrictions
O FTP hides the details of individual computer systems

51. FTP Working Mode

52. FTP Installation
O Step 1: Install the vsftpd package:
O [root@localhost Desktop] # yum
install vsftpd
O Step 2: Configure the software:
O [root@localhost Desktop] # vim
/etc/vsftpd/vsftpd.conf
O Step 3: Starting the service:
O [root@localhost Desktop] #
systemctl start vsftpd

53. Web Server
O A Web server is a program that generates and
transmits responses to client requests for Web
resources.
O Handling a client request consists of several key
steps:
O Parsing the request message
O Checking that the request is authorized
O Associating the URL in the request with a file
name
O Constructing the response message
O Transmitting the response message to the
requesting client

54. Apache Web Server

55. Hypertext Transfer Protocol
(HTTP)
O The Hypertext Transfer Protocol (HTTP) is an
application protocol for distributed, collaborative,
hypermedia information systems.
O HTTP is the foundation of data communication for
the World Wide Web.
O HTTP functions as a request–response protocol in
the client–server computing model
O HTTP is an application layer protocol designed within
the framework of the Internet Protocol Suite.
O HTTP resources are identified and located on the
network by uniform resource locators (URLs), using
the uniform resource identifier (URI) schemes http
and https.

56. Installation of HTPD
O Step 1: Install the httpd package:
O [root@localhost Desktop] # yum
install httpd
O Step 2: Configure the software:
O [root@localhost Desktop] # vim
/etc/httpd/conf/httpd.conf
O Step 3: Starting the service:
O [root@localhost Desktop] #
systemctl start httpd