Essential Advanced Linux Commands Every Programmer Should Master

Introduction

The author shares a set of practical, advanced Linux commands that can make scripts shorter and system‑administration tasks more efficient. Each command is illustrated with a concrete example and the exact syntax to use.

1. Using xargs for batch processing

The xargs command can take the output of one command and feed it as arguments to another, avoiding intermediate files. Example: find all .conf files and run file on each. find / -name *.conf -type f -print | xargs file The result shows the file type of each .conf file.

Another use is to combine find with tar to archive the matched files directly:

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

2. Running commands or scripts in the background

Long‑running operations such as database dumps should continue after the terminal is closed. Using nohup keeps the process alive and redirects output to a file.

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

If you prefer to hide the password, omit the trailing & and later suspend the job ( Ctrl+Z) and resume it in the background with bg. The output and any errors are written to nohup.out in the current directory.

3. Finding processes that consume the most memory

To locate memory‑hungry processes, pipe ps output to sort and display the top entries: ps -aux | sort -rnk 4 | head -20 The fourth column is the memory‑usage percentage; the last column shows the corresponding process.

4. Finding processes that consume the most CPU

Similarly, sorting by the third column reveals the highest CPU consumers: ps -aux | sort -rnk 3 | head -20 The third column is the CPU‑usage percentage.

5. Viewing multiple logs simultaneously with multitail

multitail

can display several log files in one terminal, with optional highlighting and filtering. Install it:

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: watch /var/log/secure for the keyword “Accepted” while simultaneously showing a live ping to Baidu:

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

6. Continuously pinging and logging results

To record ping output with timestamps, use awk to append the current time and redirect to a log file:

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

The log file receives one line per second.

7. Checking TCP connection states

Listing the state column of all TCP connections helps analyse whether connections are being released or if an attack is occurring:

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

8. Finding the top IPs requesting port 80

When traffic spikes, identify the IPs that most frequently access port 80. The following pipeline extracts the source IP, counts occurrences, and shows the top 20:

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

9. Using ssh for port forwarding

ssh

can forward a local port to a remote host, useful when a bastion host must access an internal service without exposing it. Example: forward local port 9200 on the bastion (192.168.1.15) to Elasticsearch’s 9200 on 192.168.1.19.

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

After the command, connecting to 192.168.1.15:9200 actually reaches 192.168.1.19:9200. The prerequisite is that SSH keys have been exchanged.