When we are dropped in a terminal of a server we will need to gather basic information on the system using the below commands:
1- How to know the which OS we are in ?
cat /etc/os-release
2- How to know which kernel we are using ?
uname -r
3- How much RAM does the system has ?
free -h
4- CPU type and how many cores ?
lscpu
5- Disk and Storage info ?
lsblk
df -h
6- What's my IP Address ?
ip a
curl ifconfig.me
dig +short myip.opendns.com @resolver1.opendns.com
1- To create a new ssh key:
ssh-keygen
To create a new ssh key with a different path run the above command and supply the path to the file.
2- To access the system with the key we generated:
ssh -i /path/to/file user@host -p port
3- ssh config file can be used to organise our remote servers like so :
Host server1
HostName 1.2.3.4
Port 22
User ubuntu
IdentityFile ~/.ssh/key.pem
1- How to create files ?
touch filename
touch file{1,2,3,4}
touch dir{1,2,3,4}
mkdir code
mkdir code/main/app -p
fallocate -l 1G file.txt
echo "Hello" > file.txt
2- How to list files ?
| command | description |
|---|---|
ls |
short listing |
ls -l |
long listing |
ls -a |
show hidden files |
ls -lt |
list by date |
3- How to merge several commands together ?
ls -lat | head
4-Navigate lots of files in a directory ?
ls -l | head -n 40
ls -l | tail -n 40
5- basic navigation:
/home/username/app = ~/app
cd /home/amr/app
cd ~/app
cd -
to return to the previous location
6- To sort files or directories :
ls -l | sort
7- remove duplicate files or directories ?
ls -l | sort | uniq
8- find certain files or directories ?
find /path/ -type f -iname code.txt
execute command after find:
find . -type d -exec ls -l {} \;
9- find patterns in files :
grep -i PATTERN FILE
To counnt the number of lines :
grep -i cron /var/log/syslog | wc -l
9- To properly view logs:
tail -f /path/to/log/file
less /path/to/log/file
1- To view running processes with auto refresh:
top
2- To print out running processes:
ps aux
ps ajxf
3- To view currently listening ports:
ss -tulpn
1- Print out path permission :
namei -l /var/log/syslog
2- What does chmod 755 mean ?
| item | description | numeric value |
|---|---|---|
| r | read access | 4 |
| w | write access | 2 |
| x | execution access | 1 |
Permissions are evaluated as follows :
drwxr-xr-x
d: indiated directory, if blank means file
rwx: are owner permissions
r-x: are group permissions
r-x: are others permision
3- To get the size of a directory :
du -sh /path/to/dir
better is to install ncdu package
ncdu -x /
4- soft link and hard link :
soft link is like a shortcut
ln -s TARGE LINK_NAME
Hard link is making an exact copy of something, but it doesn't take extra disk space
ln TARGE LINK_NAME
5- search for a keyword in a directory :
grep -irl /path/ -e "keyword"
6- copy files around:
cp -ar dir1 dir1_copy
rsync is widely used to transfer files
rsync -avhHp source/ destination/
rsync -avhHp -e "ssh -p22" source/ destination/
v: verbose
h: output is human readable
H: preserve hard links
p: preserve permissions
e: can supply ssh specific options
for testing use --dry-run
7- Use .bashrc to execute commands at shell login
echo "welcome $USER"
8- history is used to display terinal history for a user