Basic Linux Admin

1
Basic Linux Admin

• Tasks of Linux admin
• managing hardware
• managing the kernel
• managing filesystems
• managing user account
• managing network and security
• managing backup/installation/archiving

2
Basic Linux Administration

• Reference Guide
• System Administration
• File System Structure
• Boot Process, Init and Shutdown
• The ext3 File System
• Network Administration
• TCP Wrappers and xinetd
• Network Scripts
• Firewalling with iptables

3
File System in Linux

• Built-in hierarchical file structure
• Common directories
• /bin essential command binaries which may be
  used by the system administrator and by ordinary
  users, required for system boot
• /boot kernel image and configuration files used
  by boot loader
• /dev device files
• /etc host-specific configuration files
• /home user home directories
• /lib essential shared lib and kernel modules

4
File System in Linux (2)

• /mnt mount point for temporarily mounting files
  system such as those on a CDROM or floppy disk
• /opt add-on application software packages
• /root the root users home directory
• /sbin system binaries, essential for system
  administration, but not for system boot
• /tmp location of temporary files
• /usr secondary hierarchy, intended as sharable,
  read-only data
• /var variable data such as spool directories
  log file

5
File system

• in unix, a filesystem is some device that is
  formatted to store files. It can be found on hard
  drives, floppies, CD-ROMs and others
• the exact format and means the files are stored
  are not important
• based on second extended filesystem, ext2fs
• provide a common interface for all filesystem
  types that it recognizes

6
Ext3 file system

• In Linux 7.2, ext2 is the default file system
• Require check for consistency (e2fsck) when
  system is not properly shut down
• Ext gt ext2 gtext3
• Support 256 char filenames, 4 Tbyte max filesize
• Others MS-Dos, FAT32, NTFS, ISO9660
• Starting from Linux 7.3, ext3 is the default file
  system
• Provide stronger data integrity in event of
  unclean shutdown
• Check for consistency is needed only on rare
  hardware failure
• Higher throughput, as it is optimizes hard drive
  head motion
• Provide easy transition from ext2 to ext3
• other common filesystem are MS-DOS (FAT32, NTFS,
  ISO9660)

7
Creating user account

• manage users and group accounts and related
  system files
• passwd and group
• user account information is stored in /etc/passwd
• each line in /etc/passwd contain a username,
  password, UID, GID, users name, home directory
  and default shell
• group information is stored in /etc/group
• each line in /etc/group contain a group name,
  group password, GID and group member list

8
Creating user account

• to prevent users from obtaining encrypted
  passwords from passwd and group, show files are
  implemented
• encrypted passwords are moved to a new file,
  which is readable only by root
• the shadow file for /etc/passwd is /etc/shadow
• the shadow file for /etc/group is /etc/gshadow

9
Creating user account

• Three methods
• modify the files directly, not recommended
• Login in as root
• Create a record for the user in /etc/passwd
• Set the users password
• Specify a login shell for the user
• Create a home directory for the user
• Use command line
• useradd -D -g default_group -b default_home
  -s default_shell
• Donaldx503503unka Donald home/donald/bin/bas
  h
• Alternatively, use GUI (most recommended)

10
Daemon

• Commands to works with networks and system
  resource
• Must be continuously running a server process in
  the background, waiting to handle the users
  request
• Example
• named - translates numeric IP addresses into the
  alphanumeric names
• lpd - sends documents to a printer, over a
  network
• ftpd - allows you to connect to another machine
  via ftp

11
configuration files

• bash uses a number of configuration to set its
  operating environment when it starts
• /etc/profile
• system wide initiation files, execute during log
  in, contains environment variables, such as
  initial PATH, and startup program
• /etc/bashrc
• system wide initiation files for a user, contains
  alias

12
/etc contains host-specific configuration files

• /etc/login.defs
• /etc/conf.modules
• /etc /printcap
• /etc /x11/xdm
• /etc /x11/fs/config
• /etc /inittab
• /etc /x11/twm/system.tmw
• /etc /exports
• /etc /hot.conf
• /etc /nsswitch.conf
• /etc /network
• /etc/inetd.conf
• /etc/host.allow
• /etc/host.deny
• /etc/sendmaicf

• /etc/rc.d
• /etc/rc.sysinit
• /etc/rc
• /etc /init.d
• /etc /rc0.d
• /etc /rc1.d
• /etc /rc2.d
• /etc /rc3.d
• /etc /rc5.d
• /etc /rc6.d
• /etc /bashrc
• /etc /profile
• /etc/fstab

13
File Permission

• Every file and directory in UNIX/Linux has read,
  write, and execute permissions.
• Read permission means that the file can be read
  but not modified or deleted
• Write permission means that the file can be
  created, modified, or deleted
• Execute permission means that the file can be
  executed.

14
who use the files?

• There are 3 sets of permissions for every file or
  directory -- owner, group, and others
• The owner permissions are for the owner of the
  file or directory
• The group permissions are for everyone in the
  group
• Others The global permissions are for anyone
• What is the command to see the permission and who
  own the files?
• ans ls -l

15
chmod

• r -- file can be read
• w -- file can be written and modified
• x -- file can be executed (if it is a program)
• chmod is a standard command that allows you to
  change the permissions of a file or directory.
• There are two arguments for chmod
• the permissions based on numbers
• 1 stands for execute.2 stands for write.4
  stands for read.
• the file/directory name. The permission argument
  for chmod.

16
chmod

• chmod 777 lab2file will allow EVERYBODY full
  access to read, write and execute.
• chmod 644 lab2file will all the owner (you) read
  and write access, the group read access, and
  everybody else (world) read access too.
• chmod 700 lab2file will give yourself full access
  while giving everybody

17
Quiz 1

• Which of the following commands can be used to
  check an ext2 filesystem?
• a fsck -ext2 /dev/hda5
• b fsck /dev/hda5
• c e2fsck /etc/hda5
• d fsck.ext2 /dev/hda5
• e fsck.linux /dev/hda5

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Quiz 2

• Of the following directories, which one is most
  important to back up on a routine basis?
• a /var
• b /tmp
• c /usr
• d /root
• e /etc

19
Quiz 3

• Which one of the following commands would be best
  suited to mount a CD-ROM containing a Linux
  distribution, without depending on any
  configuration files?
• a mount /dev/cdrom /dev/hdc
• b mount -f linux /dev/hdc /mnt/cdrom
• c mount -t iso9660 /dev/cdrom /mnt/cdrom
• d mount -t linux /dev/cdrom /mnt/cdrom
• e mount -t iso9600 /mnt/cdrom /dev/cdrom

20
Quiz 4

• User jode, a member of finance group, owns a text
  file with group owner finance and mode 0077.
  Which statements are true regarding access to
  view the contents of the file, assuming the
  directory that contains it has mode 0777? Select
  all that apply.
• a. jode can view files contents
• b. jode can first change the protection mode of
  the file and then view the files contents
• c. root cannot view the files contents
• d. Everyone in the finance group can view the
  files contents except jode
• e. Everyone in the finance group can view the
  files contents including jode