Chapter 1
What is Linux?
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Linux
is the best-known and most-used open source operating system. As an
operating system, Linux is software that sits underneath all of the other
software on a computer, receiving requests from those programs and relaying
these requests to the computer’s hardware.
Some
important directories:
- /bin : All the executable binary programs (file) required during booting, repairing, files required to run into single-user-mode, and other important, basic commands viz., cat, du, df, tar, rpm, wc, history, etc.
- /boot : Holds important files during boot-up process, including Linux Kernel.
- /dev : Contains device files for all the hardware devices on the machine e.g., cdrom, cpu, etc
- /etc : Contains Application’s configuration files, startup, shutdown, start, stop script
for every individual program
- /opt : Optional is abbreviated as opt. Contains third party
application software. Viz., Java, etc.
- /sbin : Contains binary executable programs, required by System Administrator, for Maintenance.
Viz., iptables, fdisk, ifconfig, swapon, reboot,
etc.
- /usr :
Contains executable binaries, documentation, source
code, libraries for
second level program.
- /var :
Stands for variable. The contents of this file is expected to grow. This directory
contains log, lock, spool, mail and temp files.
Chapter 2
Basic Commands
· ls ,
ls –lt , ls –lr , ls –ld
· cd,
cd /home/ , cd .. , cd –
· pwd
· touch,
view , more, cat , head ,tail
· cp,
mv, diff
· df
–h, du –h
· find
/ -name *file*
· grep,
awk , xargs
· chmod,
chown
· mkdir,
rm –r
· telnet
Chapter 3
Diff btw su and sudo
Linux System is much secured than any of its counterpart. One of the way to implement security in Linux is the user management policy and user
permission and normal users are not authorized to perform any system
operations.
If a normal user needs to perform any system wide
changes he needs to use either ‘su‘ or ‘sudo‘ command.
su – need root passwd
sudo – execute system commands without root passwd
Entry in /usr/sbin/visudo file is needed in order to run the
command.
%addm,%gbladdmgrp ALL=(root) NOPASSWD: /bin/netstat
Chapter 4
Network Interface
#cd /etc/sysconfig/network-scripts/
# more ifcfg-enp0s3
TYPE=Ethernet
BOOTPROTO=dhcp
DEFROUTE=yes
PEERDNS=yes
PEERROUTES=yes
IPV4_FAILURE_FATAL=no
IPV6INIT=yes
IPV6_AUTOCONF=yes
IPV6_DEFROUTE=yes
IPV6_PEERDNS=yes
IPV6_PEERROUTES=yes
IPV6_FAILURE_FATAL=no
NAME=enp0s3
DEVICE=enp0s3
ONBOOT=yes
HWADDR=08:00:27:d3:46:62
NM_CONTROLLED=no
# more ifcfg-enp0s8
TYPE=Ethernet
BOOTPROTO=static
DEFROUTE=yes
PEERDNS=yes
PEERROUTES=yes
IPV4_FAILURE_FATAL=no
IPV6INIT=yes
IPV6_AUTOCONF=yes
IPV6_DEFROUTE=yes
IPV6_PEERDNS=yes
IPV6_PEERROUTES=yes
IPV6_FAILURE_FATAL=no
NAME=enp0s8
UUID=316eed70-31ca-41c3-abdc-519d695682b4
DEVICE=enp0s8
ONBOOT=yes
GATEWAY=192.168.56.1
NETMASK=255.255.255.0
NETWORK=192.168.56.0
Chapter 5
Package Management
YUM:
1. Install a Package
#yum install firefox
2. Removing a Package
#yum remove firefox
3. Updating a Package
#yum update firefox
4. List a Package
#yum list openssh
5. Search for a package
#yum search firefox
6. Get info
#yum info firefox
7. list all installed packages
#yum list installed
8.Package containing file
#yum provides /etc/httpd/conf/httpd.conf
9. Check available updates
#yum check-update
10.Update system
#yum update
11. List enabled repositories
#yum repolist
#yum repolist all ( enabled and disabled)
Chapter 6
Increase the Swap Space
#dd if=/dev/zero of=/swapfile count=500
bs=1MiB
#chmod 0600 /swapfile
#mkswap /swapfile
#swapon
#swapon /swapfile
#swapon -s
#free -m
Above step is for other file system type
not for ext4, for ext4 follow below
Instead of dd use
#fallocate -l 500MB /swapfile
Chapter 7
Netstat Command
To find process listening on a particular
Port
# netstat -tulpn
