Class 5 gnu-Linux basic commands

Linux Basic Commands!

There are two kinds of commands used in gnu/Linux: Built-in Shell Commands and Linux Commands.
Please note: Commands might vary somewhat in syntax and usage from one distribution of Linux to another, and from one type of shell to another. The command libraries here are provided as general references. Use the 'man command' to see how a command is used in a particular shell and on your particular Linux distribution. This session doesn't covers all commands in gnu-Linux, it just covers the basic commands used to work with for a normal user! I have categorized the commands as:

1. FILE OPERATION COMMANDS
2. SYSTEM INFO
3. PROCESS MANAGEMENT
4. FILE PERMISSIONS
5. COMPRESSION
6. NETWORK
7. INSTALLATION
8. SHORTCUTS
9. SSH
10. SEARCHING
    

1)FILE OPERATIONS:

ls – directory listing
ls -al – formatted listing with hidden files
cd dir - change directory to dir
cd – change to home
'cd -' - to goto the previous directory
cd . - current directory
cd.. - previous directory
pwd – show current directory
mkdir dir – create a directory dir
rm file – delete file
rm -r dir – delete directory dir
rm -f file – force remove file
rm -rf dir – force remove directory dir *
cp file1 file2 – copy file1 to file2
cp -r dir1 dir2 – copy dir1 to dir2; create dir2 if it doesn't exist
mv file1 file2 – rename or move file1 to file2 if file2 is an existing directory, moves file1 into directory file2
ln -s file link – create symbolic link link to file
touch file – create or update file
cat > file – places standard input into file
more file – output the contents of file
head file – output the first 10 lines of file
tail file – output the last 10 lines of file
tail -f file – output the contents of file as it grows, starting with the last 10 lines

2)SYSTEM INFO:
date – show the current date and time
cal – show this month's calendar
uptime – show current uptime
w – display who is online
whoami – who you are logged in as
finger user – display information about user
uname -a – show kernel information
cat /proc/cpuinfo – cpu information
cat /proc/meminfo – memory information
man command – show the manual for command
df – show disk usage
du – show directory space usage
free – show memory and swap usage
whereis app – show possible locations of app
which app – show which app will be run by default

3)PROCESS MANAGEMENT:
ps – display your currently active processes
top – display all running processes
kill pid – kill process id pid
killall proc – kill all processes named proc *
bg – lists stopped or background jobs; resume a
stopped job in the background
fg – brings the most recent job to foreground
fg n – brings job n to the foreground

4)FILE PERMISSIONS:
we can assign permission for every file and directories.It means that we can define a file/dir as read-only,write only,execute-only or several combinations of it.

chmod octal file – change the permissions of file
to octal, which can be found separately for user,
group, and world by adding:
● 4 – read (r)
● 2 – write (w)
● 1 – execute (x)
Examples:
chmod 777 – read, write, execute for all
chmod 755 – rwx for owner, rx for group and world
For more options, see man chmod.

5)COMPRESSION:
we can compress a file/Dir to reduce its size using just simple commands, no s/w's needed like windows,be careful with the options used.

tar cf file.tar files – create a tar named file.tar containing files
tar xf file.tar – extract the files from file.tar
tar czf file.tar.gz files – create a tar with Gzip compression
tar xzf file.tar.gz – extract a tar using Gzip
tar cjf file.tar.bz2 – create a tar with Bzip2 compression
tar xjf file.tar.bz2 – extract a tar using Bzip2
gzip file – compresses file and renames it to file.gz
gzip -d file.gz – decompresses file.gz back to file

6)NETWORK:
netstat - to know the network status
ifconfig - to find the ip of our computer
ping host – ping host and output results
whois domain – get whois information for domain
dig domain – get DNS information for domain
dig -x host – reverse lookup host
wget file – download file
wget -c file – continue a stopped download

7)INSTALLATION:
To Install from source:
./configure
make
make install

dpkg -i pkg.deb – install a package (Debian)
rpm -Uvh pkg.rpm – install a package (RPM)

8)SHORTCUTS:
Ctrl+C – halts the current command
Ctrl+Z – stops the current command, resume with
fg in the foreground or bg in the background
Ctrl+D – log out of current session, similar to exit
Ctrl+W – erases one word in the current line
Ctrl+U – erases the whole line
Ctrl+R – type to bring up a recent command
!! - repeats the last command
exit – log out of current session

9)SSH:
ssh user@host – connect to host as user
ssh -p port user@host – connect to host on port
port as user
ssh-copy-id user@host – add your key to host for
user to enable a keyed or passwordless login


10)SEARCHING:
grep pattern files – search for pattern in files
grep -r pattern dir – search recursively for
pattern in dir
command | grep pattern – search for pattern in the
output of command
locate file – find all instances of file


*please use the commands careafully.Be caution with the options used.

For more options for the commands look 'man'.

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