sar 指令應用

簡介

Sar - RedHat/CentOS 內建的系統效能分析工具。

特點：

• 內建在 CentOS/RedHat 5+版本，無需另外安裝。
• 可查詢最近幾日的系統資源使用歷史紀錄，常作為事件後的問題偵錯工具。

可分析的系統資訊包含如下：

• CPU / IO / System / Nice / Idle percentages
• Network Traffic / Network Errors
• Load Average and Run queue
• Interrupts
• Memory Free / Cached / Buffered / Swapped
• Device usage per Major/Minor number
• And many others
   

官方連結：How to use SAR to Monitor System Performance in Red Hat Enterprise Linux (如無法存取連結，請見下方附檔區)

Sar 如何運作

• SAR writes to log files in /var/log/sa. This directory holds two types of files - sa\#\# files (binary) and sar\#\# files (text).
• The number at the end of the file corresponds to the day of the month that file was recording.
• For example, an sa03 file refers to the 03 day of the month.
• When the sysstat package is installed it places a file into /etc/cron.d/sysstat.
• This sets up two cron jobs.
  
  1. job to record statistics every 10 minutes.
  2. job to write the binary sa\#\# file to a text sar\#\# file once a day (typically right before midnight).
• Additionally, it places a configuration file in /etc/sysconfig/sysstat.
• 預設是保留最近七日的歷史資料，若要變更，可以修改 /etc/sysconfig/sysstat。
  Note that RHEL 4/5 sysstat does not support keeping more than 1 month of data; however, in RHEL6 if a HISTORY value greater than 28 is declared, SAR log files are automatically split up into separate directories.
   

Sar Cron Jobs：

/etc/cron.d/sysstat

# run system activity accounting tool every 10 minutes 
*/10 * * * * root /usr/lib/sa/sa1 1 1 

# generate a daily summary of process accounting at 23:53 
53 23 * * * root /usr/lib/sa/sa2 -A

If it is desired for SAR to collect data more frequently, simply change "*/10" to a new interval.

For example, if to make SAR to track every 5 minutes, simply change to "*/5".

NOTE: SAR does not add significant load to a server. It safely can be tuned down to 2 minute intervals without seeing a significant problem. SAR also does not grab individual block data.

安裝

RedHat 5/6/7

yum install sysstat

使用方法

顯示今日 CPU 狀態

// 每個處理器
sar -P ALL

// 顯示 CPU
sar -u 

顯示最近月份 13 號的網路狀態

sar -n ALL -f /var/log/sa/sa13

顯示最近一個月份 7 號 時間 10:00 - 14:00 的記憶體使用狀況，並將結果導出一個檔案

sar -r -s 10:00:00 -e 14:00:00 -f /var/log/sa/sa07 -o /tmp/mem.txt

即時監看

CPU
sar -u 1
sar -u 1 10

Memory
sar -r 1
sar -r 1 10

Swap
sar -S 1
sar -S 1 10

I/O
sar -b 1
sar -b 1 10
sar -p -d 1
sar -p -d 1 10 

線上分析器

RedHat 提供幾個透過線上的工具來分析

I/O 使用分析: https://access.redhat.com/labs/rhiou/

在系統內先執行 lsblk 將輸出內容導出一個檔案 lsblk.out，將此檔連同要分析的任一個 sarXX 檔上傳該網址，即可以圖形顯示系統 I/O 的使用狀態。

Memory 使用分析: https://access.redhat.com/labs/rhma/

延伸閱讀

• Sar command usage with examples in Linux
• The Sysadmin's Toolbox: sar