Essential Linux & Server Commands: From Log Cleanup to RAID and Monitoring

1. Delete *.log files older than three days

Use find . -ctime +3 -name '*.log' | xargs rm -rf (or directly find . -ctime +3 -name '*.log' -exec rm -rf {} +).

2. Find top 10 IPs by page requests in nginx access log

Command:

cat access.log | awk '{print $1}' | uniq -c | sort -rn | head -10

3. Capture HTTP traffic from 192.168.1.1 port 80 with tcpdump

Command:

tcpdump 'host 192.168.1.1 and port 80' > tcpdump.log

4. Print yesterday’s local time in Python

Example:

import time; print(time.strftime('%Y-%m-%d %H:%M:%S', time.localtime(time.time() - 86400)))

5. Reverse a numeric string in Python

Use slicing: '123456'[::-1] yields '654321'.

6. Execute shell commands from Python and capture output

Example using subprocess:

import subprocess
proc = subprocess.Popen('ls', shell=True, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
stdout, stderr = proc.communicate()
print(stdout)

7. Parallel execution class with multiprocessing

Example:

import multiprocessing, time
class ClockProcess(multiprocessing.Process):
    def __init__(self, interval):
        super().__init__()
        self.interval = interval
    def run(self):
        n = 5
        while n > 0:
            print("the time is {0}".format(time.ctime()))
            time.sleep(self.interval)
            n -= 1

8. Forward local port 80 to 8080 on host 192.168.2.1

iptables command:

iptables -t nat -A PREROUTING -d 192.168.2.1 -p tcp --dport 80 -j REDIRECT --to-port 8080

9. Schedule a cron job to run every 2 hours between 6 am and 12 pm in November

Cron expression:

0 6-12/2 * 11 * /usr/bin/httpd.sh

10. Move files larger than 100 KB from /usr/local/test to /tmp

Command:

find /usr/local/test -type f -size +100k -exec mv {} /tmp/ \;

Alternative script example provided.

11. RAID levels 0, 1, and 5 overview

RAID 0 : Striping for performance, no redundancy.

RAID 1 : Mirroring for redundancy, read performance boost, 50% usable capacity.

RAID 5 : Distributed parity across at least three disks, provides redundancy and improved read/write performance.

12. Oracle database backup methods

Physical backup (cold/hot) using RMAN; logical backup of tables, schemas via exp/expdp or flashback.

Backup strategies: full, incremental, differential.

13. Identify process using port 8080

Commands: netstat -anpt | grep 8080 or

lsof -i :8080

14. Apache 2.x MPM modes and module inspection

prefork : Multi‑process, one thread per process, higher memory usage, good isolation.

worker : Multi‑process with multiple threads per process, lower memory, better concurrency.

List loaded modules: httpd -M or httpd -l. Show compile‑time settings: httpd -V.

15. Monitoring tools comparison

Nagios – status monitoring via NRPE, SNMP, alerts via SMS/email.

Cacti – performance and traffic graphs via SNMP.

Zabbix – open‑source, combines features of Nagios and Cacti, supports auto‑discovery, distributed monitoring, multiple protocols.