Linux Health Check Commands

This document contains some of the commonly used linux commands when performing health check on a machine running Linux Operating System.

To view overall performance.

[root@myserver]# top

Note:
- By default is will sort processes based on CPU usage. Press "M" to sort based on memory usage.

To view I/O of storage devices.

[root@myserver]# iostat [root@myserver]# iostat -d  #Display only disk I/O statistics [root@myserver]# iostat -n  #Display on network storage devices [root@myserver]# iostat -m  #Display I/O in MB/s [root@myserver]# iostat 1 3 #Display I/O every second for 3 times

To check CPU usage at interval of 5 seconds for 3 times.

[root@myserver]# sar -u 5 3 Linux (mysever)  09/29/2013 08:31:15 PM       CPU     %user     %nice   %system   %iowait     %idle 08:31:20 PM       all     16.92      0.00      1.48      0.15     81.45 08:31:25 PM       all     14.65      0.00      0.80      0.10     84.45 08:31:30 PM       all     15.85      0.00      2.02      0.07     82.05 Average:          all     15.81      0.00      1.43      0.11     82.65

To check memory and swap utilization in megabytes.

[root@myserver]# free -m              total       used       free     shared    buffers     cached Mem:          3735       3567        168          0        270       2221 -/+ buffers/cache:       1075       2659 Swap:         8191         23       8168

To find out top 10 processes consumed the most memory.
The below command will take the output of "ps -aux", sort the memory column which is column 4 from highest value to lowest and output the first 10 results.

[root@myserver]# ps -aux |sort -nrk 4| head -10

To find out top 10 processes consumed the most CPU.
The below command will take the output of "ps -aux", sort the CPU column which is column 3 from highest value to lowest and output the first 10 results.

[root@myserver]# ps -aux |sort -nrk 3| head -10

To check how many network interface configured.

[root@myserver]# ifconfig -a eth0      Link encap:Ethernet  HWaddr 11:0B:2D:EF:07:30           BROADCAST MULTICAST  MTU:1500  Metric:1           RX packets:0 errors:0 dropped:0 overruns:0 frame:0           TX packets:0 errors:0 dropped:0 overruns:0 carrier:0           collisions:0 txqueuelen:1000           RX bytes:0 (0.0 b)  TX bytes:0 (0.0 b)           Interrupt:16 eth1      Link encap:Ethernet  HWaddr 12:0B:44:FF:47:DF           inet addr:192.0.0.1  Bcast:192.0.0.255  Mask:255.255.255.192           UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1           RX packets:1216011503 errors:0 dropped:0 overruns:0 frame:0           TX packets:4253525258 errors:0 dropped:0 overruns:0 carrier:0           collisions:0 txqueuelen:1000           RX bytes:0 (0.0 b)  TX bytes:0 (0.0 b)           Interrupt:24

To check speed of eth1.

Settings for eth1:         Supported ports: [ MII ]         Supported link modes:   10baseT/Half 10baseT/Full                                 100baseT/Half 100baseT/Full                                 1000baseT/Half 1000baseT/Full         Supports auto-negotiation: Yes         Advertised link modes:  10baseT/Half 10baseT/Full                                 100baseT/Half 100baseT/Full                                 1000baseT/Half 1000baseT/Full         Advertised auto-negotiation: Yes         Speed: 1000Mb/s         Duplex: Full         Port: Twisted Pair         PHYAD: 1         Transceiver: internal         Auto-negotiation: on         Supports Wake-on: g         Wake-on: d         Current message level: 0x000000ff (255)         Link detected: yes

To check if all hard mount filesystems are mounted properly issue command "df -h" and cross check with the file /etc/fstab.

[root@myserver]# cat /etc/fstab [root@myserver]# df -h

To check who is currently logged in.

[root@myserver]# w

To check login history.

[root@myserver]# last

To check current date & time on the server.

[root@myserver]# date

To check current and previous runlevel.
The below output indicate the current runlevel is 3 and previous was 1 [Single user].

[root@myserver]# who -r run-level 3 Sep 26 06:20 last=S

To check current and previous runlevel.
The below output indicate the current runlevel is 3 and N indicates the runlevel was not change since boot.

[root@myserver]# runlevel N 3

To reboot.

[root@myserver]# reboot or [root@myserver]# shutdown -r now or [root@myserver]# init 6

To shutdown the Operating System.
By default shutdown command will bring the Operating System to runlevel 1.

[root@myserver]# shutdown

To shutdown the Operating System and poweroff.

[root@myserver]# shutdown -h now

To cancel shutdown.

[root@myserver]# shutdown -c

To list services configured.

[root@myserver]# chkconfig --list

To start a service.

[root@myserver]# service nfs start

To view hardware info.

[root@myserver]# dmidecode