Linux Commands

Find out user's login history $ zgrep username /var/log/auth.log*
Show date with YYYYDDMM format $ date '+%Y%m%d'
Show real-time processes that the user owns $ top -u username
Show real-time processes with command arguments $ top -c
Display memory usage as the human-readable output $ free -h
Check local network by ping localhost $ ping 0
Disable the network Interface(e.g. eth0) $ sudo ifconfig eth0 down
Find files larger than 100MB in the current directory $ find . -size +100M
How to find largest files and directories in Linux $ du -a | sort -n -r | head -n 15
Create a compressed tar.gz archive file archive.tar for a directory backup in current working directory $ tar czvf archive.tar.gz ./backup/
How to POST JSON with curl $ curl -X POST -H "Content-Type: application/json" -d '{"id": "1"}' localhost:3000/api/v1/users
How to DELETE JSON with curl $ curl -X POST -H "Content-Type: application/json" -d '{"id": "1"}' localhost:3000/api/v1/users
How to GET JSON with basic authentication using curl $ curl --basic -u $username:$password -H "accept: application/json"
Reverse port forwarding with ssh to access to my home PC through the proxy server $ ssh -N -R :8000:localhost:22 username@proxy_server # at my home PC
Set permission to protects a file, foo.txt, against any access from other users, while the issuing user still has full access. $ chmod 700 foo.txt
Show date with ISO8601 format $ date --iso-8601="seconds"
Display memory usage as human readable format 3 times in 3 seconds interval $ free -h -s 3 -c 3
Enable the network Interface(e.g. eth0) $ sudo ifconfig eth0 up
Display the network settings of specific interface (e.g. eth0) $ ifconfig eth0
Display all network setting $ ifconfig
Perform a full-format listing of the process status $ ps -ef
List subdirectories only n level[s] deep $ find -maxdepth N
Execute a task as a background job specifying dyno size with rails runner on Heroku $ heroku run:detached rails runner Tasks::MyTask.execute --app myapp --size=standard-2x
Lauch archlinux lxd image with lxc command $ lxc launch images:archlinux/current/amd64 CONTAINER_NAME
How to search lxc images $ lxc image list images: archlinux amd64
Run expo changing hostname to run remotely $ REACT_NATIVE_PACKAGER_HOSTNAME=YOUR_HOST expo start
Copy a file from the other branch using git $ git checkout my_other_branch a_file. # e.g. git checkout feature_branch app/models/user.rb
Show all migrations on Rails $ rails db:migrate:status # or rake db:migrate:status
How to remove gitignored files from branch (bash) $ git rm --cached `git ls-files -i -c --exclude-from=.gitignore`