Lesson 1

Date: 5/30/2018
User accounts, files and directories, processes, system commands.
Linux System Administration

Systems commands

Directory Manipulation

When you login into the system, you automatically get into your home directory
1. Determine the directory you are in:
2. Go to some other directory, for example, /etc:
      cd /etc
3. Go to your home directory:
      cd $HOME
      cd ~
4. Go back-and-forth between directories and check where you are:
      cd /etc
      cd -
      cd -
5. Create a new directory above your home directory:
      mkdir Newdir
6. Go to the new directory and check where you are:
      cd Newdir
7. Go one step back to the parent directory and check where you are:
      cd ..
8. Remove the new directory:
      rmdir Newdir
9. Create a new directory above your home directory with subdirectories. Try the following:
      mkdir Newdir/one/two/three
Does it work? Try the following:
      mkdir -p Newdir/one/two/three
10. Create a few files in Newdir/one:
      cd Newdir/one; touch f1.t; touch f2.t; touch f3.t
11. Go back into the original directory and try to delete Newdir:
      cd -
      rmdir Newdir
Does it work ? Try the following:
      rm -R Newdir
12. Repeat step #10; Copy the directory with its tree into another directory:
      cp -dpR Newdir Newdir-1
same as
      cp -a Newdir Newdir-1

13. Show content of file /etc/hosts
cat /etc/hosts
tac /etc/hosts
less /etc/hosts
14. Show the first and last 10 lines of a file
head -n 10 /etc/nsswitch.conf
tail -n 10 /etc/nsswitch.conf
15. Show date on the system clock
16. File system usage
df -h
17. Disk usage
du -h /home
du -s /home
du --max-depth=1 /var
du -x /
du -x /home
du -x /usr
18. Display data
echo $[10*3+2]
echo '$[10*3+2]'
echo "$[10*3+2]"
19. Determine file type
file /bin/ls
file /etc/hosts
20. Who is logined to the system
21. The owner of the current shell
22. Getting information about a file or command, for example netstat
whatis netstat
apropos netstat
man netstat
info netstat

23. Compressing/uncompressing files with gzip, and bzip2:
cd ~
cp /etc/hosts  hosts.txt
gzip hosts.txt
ls -l
less hosts.txt.gz
more hosts.txt.gz
zcat hosts.txt.gz
gzip -d hosts.txt.gz
bzip2 hosts.txt
bzip2 -d hosts.txt.bz2
24. Searching for files by using command find
cd /tmp
mkdir newfiles; cd newfiles
touch fff.txt
cd ~
find / -name fff.txt
cd /tmp
find . -name fff.txt
find . -name '*ff*'
find /tmp -name fff.txt -exec rm '{}' ';'
find /var -size +1000k
find /var -size +1000000c
find /home -user hostadm
find /var -mtime -5
find /var -maxdepth 2 -mtime -20
25. Searching for system files
which dpkg
whereis dpkg
locate dpkg

26. Using tar-gzip to archive a directory.
Create a new directory with subdirectories above your home directory, then tar and gzip it. For example,
mkdir -p Newdir/one/two/three
cd Newdir/one/two
cp /etc/hosts .
cd three
cp /etc/passwd .
cd ~
tar -cvf Newdir.tar Newdir
gzip Newdir.tar
ls -l Newdir.tar.gz
rm -R Newdir
cp Newdir.tar.gz /tmp
cd /tmp
gzip -d Newdir.tar.gz
tar -xvf Newdir.tar
27. To tar and gzip file with one command, try the following:
tar -zcvf Newdir.tgz Newdir
rm -R Newdir
ls -l Newdir.tgz
tar -zxvf Newdir.tgz
28. Archive/restore from input file list by cpio command:
cd /etc
find . | cpio -ov  > /tmp/etc.cpio
mkdir /tmp/RESTORE
cd /tmp/RESTORE
cpio -iv < ../etc.cpio

29. Command history in bash shell:
Find a command in the history by the regular expression in its name:
ctrl + R
then type the string contained in the command.
30. Command history file .bash_history is updated when a user exits the shell.
tail .bash_history
The size or file .bash_history is defined by env variable HISTSIZE

  • Reference: Basic System Commands

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