Several cheat-sheets of different topics in .md format. Checkout the Github pages version.
Print out the running processes:
ps -ef
Also, we can use the top command
top
With top running, we can type h to open the help menu.
We can track processes triggered by a specific user calling top as follows:
top -u username
For example, typing V we can toggle the view to view a forest tree process hierarchy.
Sort percentage of CPU’s usage by user and process
ps -eo pcpu,pid,user,args | sort -r -k1 | less
A fancier top
htop
Sort processes by start time:
ps -ef --sort=start_time
Processes of a given user:
ps -fu username
ps -fu username --sort=start_time
Check logs/Status of a process
journalctl -u httpd.service
Start a service
systemctl start a_service.service
Stop a service
systemctl stop a_service.service
Check system time:
timedatectl
Set local date time:
timedatectl set-timezone Europe/Madrid
Schedule a script run with a given user. As the user run
crontab -e
Example (run everyday a script at 13:55 h):
55 13 * * * /home/ec2-user/script_path/run-cleanhouse.sh
Check logs:
less /var/log/cron
Look to which services use logrotate
/etc/logrotate.d/
Sometimes apache web server may be restarted/reloaded, check it in /etc/logrotate.d/httpd.
Get the ip address:
hostname -I
Check if a remote host is accessible from the current one via a specific port number:
exec 3<> /dev/tcp/180.18.153.59/7222
if there is not a [Connection timed out], then it is accessible. Output can be checked with echo $?.
Find all lines that contain a pattern
grep -option pattern file
Option can be i if you want to ignore uppercase characters.
Option can be A N if you want to retrieve the N lines after each match
Option can be B N if you want to retrieve the N lines before each match
Option can be C N if you want to retrieve the N lines around each match
File can be * for all files in the working directory.
File can be -r to search recursively in all files and directories contained in the working directory.
Find all files with a given name pattern inside a folder
find /folder -type f -name '*.html'
By exact name
find -type f -name exact-name.ext
Display json contents pretty:
pyhon -m json.tool json_file.json
Create a symbolic link
ln -s {source-filename} {symbolic-filename}
Create a tarball file without compression of a folder in a different folder (note the ordering, destination goes first!)
tar -cvf PATH_TO_DESTINATION_FILE.tar SOURCE_FOLDER_1 SOURCE_FOLDER_2 ... SOURCE_FILE_1 SOURCE_FILE_2 ...
Use compression
tar -cvzf PATH_TO_DESTINATION_FILE.tar.gz SOURCE_FOLDER_1 SOURCE_FOLDER_2 ... SOURCE_FILE_1 SOURCE_FILE_2 ...
List the contents of a tar file
tar -ztvf TARFILE
Unroll a tarball specifying the destination folder
tar -xvf TARFILE -C DESTINATION_FOLDER
Zip a folder
zip -r "$zip_file" "$temp_dir"
Zip with password
zip -P "$zip_password" -r "$zip_file" "$temp_dir"
Flatten files in folder (omit folder itself in zip file)
zip -P "$zip_password" -r -j "$zip_file" "$temp_dir"
Ssh using an existing private key .pem file
ssh -i "path_to_pem_file" user@dns
Generate a key pair… [TODO]
Generate a public key from an already existing private key:
ssh-keygen -y -f id_rsa > id_rsa.pub
Migrate an already existing key:
cd .ssh
touch id_rsa
vi id_rsa # paste content of private key .pem file and save
chown user:group id_rsa # the user authenticating must be the owner of the key
chmod 600 id_rsa # permissions must be read/write only for the key owner
For a specific user, the key pairs are stored in the corresponding home under .ssh, e.g.,
/home/ec2-user/.ssh
/var/lib/jenkins/.ssh
on .ssh the id_rsa is the private key and id_rsa.pub is the public key.
The public key file contains one line which is the public key indeed.
Note that any possible destination host must have this public key included in its authorized_keys file, also inside .ssh.
If you bring an already existing key to a new user, you should create the id* files as the user and copy the keys. Finally, they need to have 600 permissions:
sudo chmod 600 $privateKeyFile
sudo chmod 600 $publicKeyFile
Create a new one using the terminal
export NEWVAR="something"
Delete an existing environment variable:
unset NEWVAR
You can also add the variables permanently to the environment
echo 'NEWVAR="content/asdf"' >> /etc/environment
echo 'PUBLIC_IP='$PUBLIC_IP >> /etc/environment
Create a group
sudo groupadd jenkinsGroup
Add an existing user to a group
sudo usermod -a -G ec2-user jenkins
Display all users
cat /etc/passwd
Display user groups
id ec2-user
Create a new user and assign groups in a single command
sudo useradd -g primary_group -G sec_groupA,sec_groupB new_user
Change to a user of a service account (without shell by design), such as jenkins user. It is necessary to specify the shell explicitly in these cases:
sudo su -s /bin/bash jenkins
export PATH=new_path:$PATH
To see which directory is used for a program
which python
Define alias
alias aliasname='some command'
A useful method is to gather aliases in files ~/.bash_aliases, then load them during profile adding to ~/.profile or ~/.bashrc the following
# Alias definitions.
# You may want to put all your additions into a separate file like
# ~/.bash_aliases, instead of adding them here directly.
# See /usr/share/doc/bash-doc/examples in the bash-doc package.
if [ -f ~/.bash_aliases ]; then
. ~/.bash_aliases
fi
Aliases are declared between single quotes.
When using awk, the print part goes also between single quotes:
cat file.txt | grep 'log-2' | awk -F ; '{print $2}'
To use the awk command above in an alias we should write single quotes ' as '\'':
alias an_awk_command='cat file.txt | grep '\''log-2'\'' | awk -F ; '\''{print $2}'\'''
Continue to bash - part 2
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