Essential Linux Commands for Database Monitoring and System Management

Querying Oracle client connections

Use netstat combined with grep and awk to list client IPs that are connected to a specific Oracle SID or listening on port 1521:

netstat -anpT | grep oracleSID | awk '{print $5}' | grep -o -E '1.*:' | awk -F ':' '{print $1}' | sort

netstat -anpT | grep 1521 | awk '{print $5}' | grep -o -E '1.*:' | awk -F ':' '{print $1}' | sort

Killing unwanted processes

Terminate processes that are connected to a given Oracle SID:

kill -9 `ps -ef | grep oracleSID | grep LOCAL=NO | grep -v grep | awk '{print $2}'`

Or kill all processes owned by a specific user (e.g., userA):

pkill -9 -u userA

Counting connections and processes

Number of processes listening on port 1521: netstat -pan | grep 1521 | wc -l Number of processes coming from a particular host (e.g., 192.168.21.15):

netstat -pan | grep 192.168.21.15 | wc -l

Summarizing client IP traffic on port 1521

Two equivalent pipelines produce a ranked list of client IPs and their connection counts:

netstat -apnT | grep 1521 | awk '{print $5}' | sort -u | grep -v 1521 | grep -v '*' | awk -F ':' '{print $4}' | uniq -c | sort -nr

netstat -anpT | grep 1521 | awk '{print $5}' | grep -o -E '1.*:' | awk -F ':' '{print $1}' | sort | uniq -c | sort -nr

File system size checks

Show the top 10 largest files or directories in the current folder: du -s * | sort -nr | head Calculate total size of log files created on a specific date (example for 2016‑05‑09):

ls --full-time `find ./* -name "log_*.bak"` | grep '2016-05-09' | awk '{print $9}' | xargs du -ck

Delete files older than a given number of days (e.g., 150 days) or matching a pattern:

find /mitac/mds/arch/ -ctime +150 -exec rm -rf {} \;

find /mitac/mds/arch/ -name '*836701255.dbf' -ctime +150 -exec rm -rf {} \;

Process resource usage

Top 10 CPU‑intensive processes:

ps auxw | head -1; ps auxw | sort -rn -k3 | head -10

Top 10 memory‑intensive processes:

ps auxw | head -1; ps auxw | sort -rn -k4 | head -10

Top 10 processes using the most virtual memory:

ps auxw | head -1; ps auxw | sort -rn -k5 | head -10

In top, press 1 to view per‑CPU stats, Shift+P to sort by CPU, and Shift+M to sort by memory.

Useful one‑liners

Replace all occurrences of 1 with 2 in vi: :%s/1/2/g Display I/O statistics every second for three intervals, with values in MB: iostat -d -x -m 1 3 Measure how long it takes to copy a file: time cp file1 /u01/ Show CPU usage between 07:00 and 10:00 using sar:

sar -s 07:00:00 -e 10:00:00