diffrent kinds of linux branches with the same linux core,are called distros.like ubuntu,fedora,debian.
packages
softwares are packaged to easily be installed.
debian based packages are in .deb format
whereas redhat based are rpm packages.
Repositories
It is a software packages container.
when search via software centre or tools lke apt-get or yum,
you are shown a list of the packages within the repositories available to your system.
A sofware repository can store its files on one server or across different servers known as mirrors.
These are various Linux repo mirrors. They are unlisted, but public to anyone who needs them.
PPA
personal package archives -- PPAs provide access to third-party programs.
. These offer software not bundled in a default Linux operating system.
How to Add a PPA?
sudo add-apt-repository [repository name]
sudo apt-get update
sudo apt-get install [software name]
/ is called superuser home directory.It is the top of file system structure.All other directory are mounted under it.
/boot contain the kernal image file.This also contain the files related to booting the system such as bootloader.
/etc contain the whole system configuration file.
/home This is the all users home directory.
/mnt This is a generic mount point under which you mount your filesystems such as cdrom,floppy.
/proc It is not a real file system, it is a virtual file system.This directory is empty until the proc file system is mounted.
/sys Modern Linux distributions include a /sys directory as a virtual filesystem (sysfs, comparable to /proc, which is a procfs),
which stores and allows modification of the devices connected to the system.
/dev contain the devices nodes through which the operating system can access hardware and software devices on the system.
/bin contain the command used by superuser and normal user.
/sbin ontain the command used by superuser only
/var/www/html/ contain php files for local web host (lamp)
Backing up partition is nothing but actually backing up MBR (master boot record).
The command is as follows for backing up MBR stored on /dev/sdX or /dev/hdX :
# dd if=/dev/sdX of=/tmp/sda-mbr.bin bs=512 count=1
( Replace X with actual device name such as /dev/sda.)
To restore partition table to disk, all you need to do is use dd command:
# dd if= sda-mbr.bin of=/dev/sdX bs=1 count=64 skip=446 seek=446
How To Install Linux, Apache, MySQL, PHP (LAMP) stack on Ubuntu 18.04
Shell commands
Shell commands are part of the shell program.
There are several different shells
(C shell, bash shell, bourne shell etc) to choose from,
and each will have a variation of the shell commands built in.
The commands vary between shells,
but each shell is the same across different linux distros.
To remove package called mplayer, enter:
$ sudo apt-get remove mplayer
Uncompressing content of a file :
tar -xvzf Komodo
make a program from its source files:
sh ./configure
Directory operations ::
ls to list - the names of the directories and files in the current directory
cp -r dir1 dir22 - to copy all contents of dir1 to dir2 recurcievly
rm -f -r {file-name} - To remove a file or directory
Where, -f: Forcefully remove file and -r: Remove the contents of directories recursively
linux permissions
SYSTEM INFORMATION
uname -a Display Linux system information
uname -r Display kernel release information
cat /etc/redhat-release Show which version of redhat installed
uptime Show how long the system has been running + load
hostnameShow system host name
hostname -I Display the IP addresses of the host
last reboot Show system reboot history
Show the current date and time
date
Show this month's calendar
cal
Display who is online
w
Who you are logged in as
whoami
HARDWARE INFORMATION
Display messages in kernel ring buffer
dmesg
Display CPU information
cat /proc/cpuinfo
Display memory information
cat /proc/meminfo
Display free and used memory ( -h for human readable, -m for MB, -g for GB.)
free -h
Display PCI devices
lspci -tv
Display USB devices
lsusb -tv
Display DMI/SMBIOS (hardware info) from the BIOS
dmidecode
Show info about disk sda
hdparm -i /dev/sda
Perform a read speed test on disk sda
hdparm -tT /dev/sda
Test for unreadable blocks on disk sda
badblocks -s /dev/sda
PERFORMANCE MONITORING AND STATISTICS
Display and manage the top processes
top
Interactive process viewer (top alternative)
htop
Display processor related statistics
mpstat 1
Display virtual memory statistics
vmstat 1
Display I/O statistics
iostat 1
Display the last 100 syslog messages (Use /var/log/syslog for Debian based systems.)
tail 100 /var/log/messages
Capture and display all packets on interface eth0
tcpdump -i eth0
Monitor all traffic on port 80 ( HTTP )
tcpdump -i eth0 'port 80'
List all open files on the system
lsof
List files opened by user
lsof -u user
Display free and used memory ( -h for human readable, -m for MB, -g for GB.)
free -h
Execute "df -h", showing periodic updates
watch df -h
USER INFORMATION AND MANAGEMENT
Display the user and group ids of your current user.
id
Display the last users who have logged onto the system.
last
Show who is logged into the system.
who
Show who is logged in and what they are doing.
w
Create a group named "test".
groupadd test
Create an account named john, with a comment of "John Smith" and
create the user's home directory.
useradd -c "John Smith" -m john
Delete the john account.
userdel john
Add the john account to the sales group
usermod -aG sales john
5 – FILE AND DIRECTORY COMMANDS
List all files in a long listing (detailed) format
ls -al
Display the present working directory
pwd
Create a directory
mkdir directory
Remove (delete) file
rm file
Remove the directory and its contents recursively
rm -r directory
Force removal of file without prompting for confirmation
rm -f file
Forcefully remove directory recursively
rm -rf directory
Copy file1 to file2
cp file1 file2
Copy source_directory recursively to destination.
If destination exists, copy source_directory into destination,
otherwise create destination with the contents of source_directory.
cp -r source_directory destination
Rename or move file1 to file2. If file2 is an existing directory,
move file1 into directory file2
mv file1 file2
Create symbolic link to linkname
ln -s /path/to/file linkname
Create an empty file or update the access and modification times of file.
touch file
View the contents of file
cat file
Browse through a text file
less file
Display the first 10 lines of file
head file
Display the last 10 lines of file
tail file
Display the last 10 lines of file and "follow" the file as it grows.
tail -f file
PROCESS MANAGEMENT
Display your currently running processes
ps
Display all the currently running processes on the system.
ps -ef
Display process information for processname
ps -ef | grep processname
Display and manage the top processes
top
Interactive process viewer (top alternative)
htop
Kill process with process ID of pid
kill pid
Kill all processes named processname
killall processname
Start program in the background
program &
Display stopped or background jobs
bg
Brings the most recent background job to foreground
fg
Brings job n to the foreground
fg n
FILE PERMISSIONS
Linux chmod example
PERMISSION EXAMPLE
U G W
rwx rwx rwx chmod 777 filename
rwx rwx r-x chmod 775 filename
rwx r-x r-x chmod 755 filename
rw- rw- r-- chmod 664 filename
rw- r-- r-- chmod 644 filename
NOTE: Use 777 sparingly!
LEGEND
U = User
G = Group
W = World
r = Read
w = write
x = execute
- = no access
NETWORKING
Display all network interfaces and ip address
ifconfig -a
Display eth0 address and details
ifconfig eth0
Query or control network driver and hardware settings
ethtool eth0
Send ICMP echo request to host
ping host
Display whois information for domain
whois domain
Display DNS information for domain
dig domain
Reverse lookup of IP_ADDRESS
dig -x IP_ADDRESS
Display DNS ip address for domain
host domain
Display the network address of the host name.
hostname -i
Display all local ip addresses
hostname -I
Download http://domain.com/file
wget http://domain.com/file
Display listening tcp and udp ports and corresponding programs
netstat -nutlp
ARCHIVES (TAR FILES)
Create tar named archive.tar containing directory.
tar cf archive.tar directory
Extract the contents from archive.tar.
tar xf archive.tar
Create a gzip compressed tar file name archive.tar.gz.
tar czf archive.tar.gz directory
Extract a gzip compressed tar file.
tar xzf archive.tar.gz
Create a tar file with bzip2 compression
tar cjf archive.tar.bz2 directory
Extract a bzip2 compressed tar file.
tar xjf archive.tar.bz2
INSTALLING PACKAGES
Search for a package by keyword.
yum search keyword
Install package.
yum install package
Display description and summary information about package.
yum info package
Install package from local file named package.rpm
rpm -i package.rpm
Remove/uninstall package.
yum remove package
Install software from source code.
tar zxvf sourcecode.tar.gz
cd sourcecode
./configure
make
make install
SEARCH
Search for pattern in file
grep pattern file
Search recursively for pattern in directory
grep -r pattern directory
Find files and directories by name
locate name
Find files in /home/john that start with "prefix".
find /home/john -name 'prefix*'
Find files larger than 100MB in /home
find /home -size +100M
SSH LOGINS
Connect to host as your local username.
ssh host
Connect to host as user
ssh user@host
Connect to host using port
ssh -p port user@host
FILE TRANSFERS
Secure copy file.txt to the /tmp folder on server
scp file.txt server:/tmp
Copy *.html files from server to the local /tmp folder.
scp server:/var/www/*.html /tmp
Copy all files and directories recursively from server to the
current system's /tmp folder.
scp -r server:/var/www /tmp
Synchronize /home to /backups/home
rsync -a /home /backups/
Synchronize files/directories between the local and remote system
with compression enabled
rsync -avz /home server:/backups/
DISK USAGE
Show free and used space on mounted filesystems
df -h
Show free and used inodes on mounted filesystems
df -i
Display disks partitions sizes and types
fdisk -l
Display disk usage for all files and directories in human readable format
du -ah
Display total disk usage off the current directory
du -sh
DIRECTORY NAVIGATION
To go up one level of the directory tree. (Change into the parent directory.)
cd ..
Go to the $HOME directory
cd
Change to the /etc directory
cd /etc
Linux Commands
Linux commands are not part of the shell.
Each one is a seperate executable program,
probably written in the C programming language.
These executables are stored in various directories
set up for binary files, such as /bin and /usr/bin.
The location of these directories can be defined with the $PATH variable
so the shells know where to find them.
These commands vary between different linux distrubutions,
and remain the same whichever shell you are using.
grep
grep prints the lines from a file or input stream
that match an expression.
For example, if you want to print the lines in the
/etc/passwd file that contain the text root, use this command:
grep root /etc/passwd
The grep command is extraordinarily handy
when operating on multiple files at once,
because it prints the filename in addition to the matching line
when in this multiple-file mode.
For example, if you want to check on every file in /etc that
contains root, you could use this command:
grep root /etc/*
more and less
When a command's output is long, it can scroll off the top of the screen,
and it's annoying to use a scrollbar to view such output because you have to move your hands around.
You sometimes may also want to look at a large text file without starting a text editor.
Two standard commands for text navigation are more and less.
To page through a big file like /usr/dict/words, use a command such as more /usr/dict/words.
When running more, you will see the contents of the file, one screenful at a time.
You can press the space bar to go forward in the file and the b key to skip back one screenful.
To quit more, type q.
The less command performs the same function as more, but it is far more powerful and widely used.
Use less --help to get a good summary of its operations.
As you will learn in Section 1.14, you can send the output of nearly any program directly
to another program's input, enabling operations such as this (try it to see what it does):
grep ie /usr/dict/words | less
pwd
This program's name stands for "print working directory,"
and the command outputs the current working directory.
That's all that pwd does, but it's useful.
Some Linux distributions set up accounts with the current working directory in the prompt,
but you may wish to change that because the current working directory takes up a lot of space on a line.
diff
To see the differences between two text files, use diff:
diff file1 file2
There are several options that can control the format of the output, such as -c,
but the default output format is often the most comprehensible (for human beings, that is).
file
If you see a file and are unsure of its format, try using file to see if the system can guess,
based on a large set of rules:
file file
You may be surprised to see how much this innocent-looking command can do.
find
It's frustrating when you know that a certain file is in a directory tree somewhere,
and you just don't know where. Run find to find file in dir:
find dir -name file -print
Like most programs in this section, find is capable of some fancy stuff.
However, don't try options such as -exec before you know the form shown here by heart,
and you know why you need the -name and -print options.
The find command accepts wildcard characters, such as *,
but you must enclose them in single quotes ('*') to protect the wildcard characters
from the shell's own wildcard features
head and tail
To quickly view a portion of a file or stream, use the head and tail commands.
For example, head /etc/inittab shows the first ten lines of this system configuration file,
and tail /etc/inittab shows the last ten lines.
You can change the number of lines to print by using the -n option,
where n is the number of lines you want to see. If you want to print lines starting at line n, use tail +n.
sort
The sort command quickly puts the lines of a text file in alphanumeric order.
If the file's lines start with numbers, and you want to sort in numeric order,
use the -n option. The -r option reverses the order of the sort.