Systems commands


Directory Manipulation

When you login into the system, you automatically get into your home directory
1. Determine the directory you are in:
      pwd 
2. Go to some other directory, for example, /etc:
      cd /etc 
3. Go to your home directory:
      cd $HOME
      or
      cd ~
4. Go back-and-forth between directories and check where you are:
      cd /etc
      pwd
      cd -
      pwd
      cd -
      pwd
5. Create a new directory above your home directory:
      mkdir Newdir 
6. Go to the new directory and check where you are:
      cd Newdir
      pwd 
7. Go one step back to the parent directory and check where you are:
   
      cd ..
      pwd
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 #9; 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
 
date 
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
who
21. The owner of the current shell
whoami
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:
history
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
echo $HISTSIZE


  • Reference: Basic System Commands