Master Essential Linux Ops: xargs, Background Jobs, Process Monitoring & More

Preface

After years of struggling with ad‑hoc scripts, the author shares concise explanations of advanced Linux commands to help both newcomers and seasoned operators write cleaner, more efficient scripts.

1. Practical xargs command

The xargs utility feeds the output of one command as arguments to another, simplifying tasks such as finding all .conf files and classifying them.

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

The result can be piped into other commands, for example to archive the files:

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

2. Running commands or scripts in background

Use nohup to keep long‑running operations alive after the terminal closes, e.g., exporting all MySQL databases:

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

If you prefer to enter the password interactively, run the command without &, then suspend it with Ctrl+Z and resume in the background with bg. Output and errors are captured in nohup.out.

3. Find processes with high memory usage

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

The fourth column shows memory‑usage percentage; the last column lists the corresponding process.

4. Find processes with high CPU usage

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

The third column indicates CPU‑usage percentage.

5. View multiple logs simultaneously

Install multitail to monitor several log files in one terminal with highlighting and filtering.

# wget ftp://ftp.is.co.za/mirror/ftp.rpmforge.net/redhat/el6/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: watch /var/log/secure for the keyword “Accepted” while simultaneously pinging Baidu:

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

6. Continuous ping logging

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

The command appends a timestamped ping line to /tmp/jiguang.log every second.

7. Check TCP connection states

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

8. Find top 20 IPs requesting 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 port 9200 on a bastion host to an internal Elasticsearch server:

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

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