Boost Your Linux Ops: Master Xargs, Background Jobs, and Advanced Monitoring Tricks

Introduction

The author shares years of ops experience and compiles useful advanced Linux commands for personal reference and to help others.

1. Practical xargs Command

Use xargs to feed the output of one command as arguments to another. Example: find all .conf files and classify them with file:

# find / -name *.conf -type f -print | xargs file

Output screenshot:

Another example packs the found files directly with tar:

# find / -name *.conf -type f -print | xargs tar cjf test.tar.gz

2. Running Commands or Scripts in Background

Use nohup to keep a command running after the terminal closes, e.g., exporting all MySQL databases:

# nohup mysqldump -uroot -pYOUR_PASSWORD --all-databases > ./alldatabases.sql &

If you prefer to enter the password interactively, run the command without &, then suspend with Ctrl+Z and resume in background with bg. The command creates a nohup.out file with logs.

3. Find Processes with High Memory Usage

Sort processes by memory percentage and show the top 20:

# ps -aux | sort -rnk 4 | head -20

4. Find Processes with High CPU Usage

Sort processes by CPU percentage and show the top 20:

# ps -aux | sort -rnk 3 | head -20

5. View Multiple Logs Simultaneously with multitail

Install multitail:

# wget ftp://ftp.is.co.za/mirror/ftp.rpmforge.net/redhat/el6/en/x86_64/dag/RPMS/multitail-5.2.9-1.el6.rf.x86_64.rpm
# yum -y localinstall multitail-5.2.9-1.el6.rf.x86_64.rpm

Example: monitor /var/log/secure for the keyword “Accepted” while simultaneously showing live ping output:

# multitail -e "Accepted" /var/log/secure -l "ping baidu.com"

6. Continuous Ping with Logging

Record a timestamped ping result every second:

ping api.jpush.cn | awk '{print $0 "    " strftime("%Y-%m-%d %H:%M:%S",systime())}' >> /tmp/jiguang.log &

The log file grows with one entry per second:

7. Check TCP Connection States

Show the count of connections per state for port 80:

# netstat -nat | awk '{print $6}' | sort | uniq -c | sort -rn

8. Top 20 IPs Requesting Port 80

Identify the most frequent source IPs for port 80:

# netstat -anlp | grep 80 | grep tcp | awk '{print $5}' | awk -F: '{print $1}' | sort | uniq -c | sort -nr | head -n20

9. SSH Port Forwarding

Forward local port 9200 on a bastion host to a remote Elasticsearch instance:

ssh -p 22 -C -f -N -g -L 9200:192.168.1.19:9200 [email protected]

After execution, accessing 192.168.1.15:9200 actually reaches 192.168.1.19:9200. Ensure SSH keys are exchanged beforehand.

Conclusion

The author will continue to add more useful Linux operations in future posts.