Linux&OSX System Commands

Linux&OSX System Commands

Get the system information (OS version): cat /etc/*-release
Lists open files and the corresponding processes: lsof -i :port
Get PID of the process which is running on specific port: netstat -nlp | grep "port"
Get the path of specific PID: ps -fp pid
Get the public ip: curl httpbin.org/ip
Read Realtime log: tailf /path/to/file
Get directory structure: tree /directory
Move to previous directory: cd - (actually it is $OLDPWD environment path)
Copy ssh public key to server: ssh-copy-id user@ip_address
Execute a command repeatedly: watch 'command'
Get the latest log: ls -larht
Manipulate compressed file with: zcat, zgrep, zless
Check if process is running: ps -ef | grep "process name"
Random password: openssl rand -base64 15
Chown with DEFAULT group: chown ownername: /path OR chown ownername. /path
Check the different: vimdiff /etc/nginx/{nginx.conf,nginx.conf.org}
Watch with alias: alias watch='watch '
Customize Login Screen Path (Ubuntu): cd /etc/update-motd.d/ --> place new login screen into here.
Customize Login Screen (CentOS): vi /etc/ssh/sshd_config --> PrintMotd no --> place new login screen to: /etc/profile.d/ --> restart
siege – An HTTP/HTTPS stress load tester
ag - the silver searcher - faster than ack
scp - daily task copy over network
rsync - save bandwidth copy over network
tldr - useful version of "man"
brew - package manager for OSX
multitail - multiple log windows
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Number Of Available Port: 
$OPENPORTS = netstat -an | grep ESTABLISHED | wc -l
cat /proc/sys/net/ipv4/ip_local_port_range => 32768 61000
=> Available Ports = 61000 - 32768 - $OPENPORTS
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