Basic Shell Commands

Common Shell Commands Collection

Quick File Writing

1. Method One

	cat > a.txt << 'EOF'
	afasdf
	EOF

2. Method Two

tee a.txt <<- 'EOF'
	afsafdsf
	EOF	

Linux System Scheduled Network Time Synchronization

Reference Article

# Set scheduled task
crontab -e 
*/5 * * * * ntpdate time.nist.gov

# View scheduled task list
crontab -l

# View scheduled task logs
tail -f /var/log/cron

# Several time servers
ntpdate time.nist.gov
ntpdate time.nuri.net
ntpdate 0.asia.pool.ntp.org
ntpdate 1.asia.pool.ntp.org
ntpdate 2.asia.pool.ntp.org
ntpdate 3.asia.pool.ntp.org

Crontab scheduled task parameter meanings

Field	Required	Allowed Values	Allowed Special Characters	Notes
Seconds	Yes	0–59	*``,``-	Standard implementation does not support this field.
Minutes	Yes	0–59	*``,``-
Hours	Yes	0–23	*``,``-
Day of month	Yes	1–31	*``,``-``?``L``W	?``L``W are only implemented by some software
Month	Yes	1–12 or JAN–DEC	*``,``-
Day of week	Yes	0–7 or SUN–SAT	*``,``-``?``L``#	?``L``# are only implemented by some software. Linux and Spring allow 0-7, where 0 and 7 are Sunday. Quartz allows 1-7, where 1 is Sunday
Year	No	1970–2099	*``,``-	Standard implementation does not support this field.

VMware Network Setup

Note: It's best to use VMware 15, VMware 16 version seems to have network issues.

Query Current Folder Total Size

du -sh ./

Query Current Directory Structure First n Level Directory Tree

Display first level directory for /d %i in (*) do @echo %i

Install lrzsz

yum install -y lrzsz

sz download, rz upload

Linux Kill Java Process

kill -9 $(ps -ef | grep -w "xxx-1.0.jar" | grep -v "grep" | awk '{print $2}')