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📌 vmstat Command in Linux

📖 Command Name & Purpose

🔹 vmstat (Virtual Memory Statistics) is a Linux command-line tool used to monitor system performance.

🔹 It provides real-time statistics on CPU usage, memory, processes, disk activity, and system I/O.

🌟 Key Features

✅ Displays CPU usage, memory statistics, and processes.

✅ Helps in performance monitoring and troubleshooting.

✅ Shows disk and I/O activity.

✅ Provides real-time updates at specified intervals.

✅ Lightweight compared to other monitoring tools like top.

📝 Basic Syntax

vmstat [options] [delay] [count]

🔹 options → Modify output format.

🔹 delay → Interval (in seconds) between updates.

🔹 count → Number of updates before stopping.

⚙️ Common Options and Their Descriptions

🔹 Command 📌 Description
vmstat 📊 Displays a one-time summary of system performance.
vmstat 2 5 ⏳ Updates statistics every 2 seconds for 5 iterations.
vmstat -s 📜 Shows detailed system statistics in a human-readable format.
vmstat -d 💽 Displays disk statistics.
vmstat -p <device> 🔍 Shows partition-specific statistics (e.g., /dev/sda).
vmstat -a 🔥 Displays active and inactive memory details.
vmstat -t 🕒 Adds a timestamp to the output.
vmstat -w 🖥️ Provides wide output format for better readability.

📌 Examples for All Switches with Explanation

1️⃣ Basic System Performance Statistics

📌 Command:

vmstat

📌 Description:

🔹 Displays a snapshot of system performance, including CPU, memory, processes, and disk activity.

📌 Output:

\e[1;36mprocs -----------memory---------- ---swap-- -----io---- --system-- -----cpu-----\e[0m
\e[1;33mr     b     swpd   free   buff  cache   si   so    bi    bo   in    cs  us  sy  id  wa  st\e[0m
\e[1;32m1     0        0  50234  12948  178920    0    0     1     5  1234  1456   2   1  96   1   0\e[0m

📌 Explanation:

  • Processes (procs): r (running), b (blocked).
  • Memory (memory): Swap (swpd), Free (free), Buffer (buff), Cache (cache).
  • CPU Usage (cpu): us (user), sy (system), id (idle), wa (waiting).

2️⃣ Real-Time Performance Monitoring

📌 Command:

vmstat 2 5

📌 Description:

🔹 Updates system statistics every 2 seconds, repeating 5 times.

📌 Output:

\e[1;36mprocs -----------memory---------- ---swap-- -----io---- --system-- -----cpu-----\e[0m
\e[1;33mr     b     swpd   free   buff  cache   si   so    bi    bo   in    cs  us  sy  id  wa  st\e[0m
\e[1;32m1     0        0  50234  12948  178920    0    0     1     5  1234  1456   2   1  96   1   0\e[0m
\e[1;32m0     0        0  50012  13010  178000    0    0     3     8  1240  1460   3   2  94   1   0\e[0m

📌 Explanation:

  • Helps track system changes over time.
  • If CPU idle (id) is low, the system might be overloaded.
  • If swap (swpd) increases, the system is using virtual memory due to low RAM.

3️⃣ Display System Memory Statistics

📌 Command:

vmstat -s

📌 Description:

🔹 Displays detailed memory statistics in a human-readable format.

📌 Output:

\e[1;33m       16 GB total memory\e[0m
\e[1;32m       12 GB used memory\e[0m
\e[1;31m        4 GB free memory\e[0m
\e[1;36m       512 MB buffer memory\e[0m
\e[1;33m       10 GB swap total\e[0m
\e[1;32m        1 GB swap used\e[0m
\e[1;31m        9 GB swap free\e[0m

📌 Explanation:

  • Total Memory → Physical RAM installed.
  • Used Memory → Memory actively used by processes.
  • Free Memory → Available RAM.
  • Swap Memory → Virtual memory usage.

4️⃣ Show Disk Statistics

📌 Command:

vmstat -d

📌 Description:

🔹 Displays disk reads, writes, and activity statistics.

📌 Output:

\e[1;36m    disk      reads   writes   sectors_read  sectors_written\e[0m
\e[1;33m    sda      10453   7890     10832040      20154321\e[0m

📌 Explanation:

  • Reads/Writes → Number of disk operations.
  • Sectors Read/Written → Amount of data processed.

5️⃣ Show Active and Inactive Memory

📌 Command:

vmstat -a

📌 Description:

🔹 Displays active and inactive memory usage.

6️⃣ Add Timestamp to Output

📌 Command:

vmstat -t

📌 Description:

🔹 Shows the current date and time in the output.

7️⃣ Wide Output for Better Readability

📌 Command:

vmstat -w

📌 Description:

🔹 Expands output columns to improve readability on wide screens.

8️⃣ Show Partition-Specific Statistics

📌 Command:

vmstat -p /dev/sda

📌 Description:

🔹 Displays disk I/O statistics for a specific partition (/dev/sda).

💡 Use Cases

🔹 Monitor CPU Usage → Detect high CPU consumption with vmstat 1 10.

🔹 Check Memory Usage → Find low memory issues with vmstat -s.

🔹 Analyze Disk Performance → View disk read/write stats using vmstat -d.

🔹 Troubleshoot System Lag → Identify high CPU load, swap usage, or disk I/O bottlenecks.