Monitoring Temperature and Fans with lm_sensors

How to install and configure lm_sensors for temp and fan monitoring

Install the lm_sensors package

sudo yum install lm_sensors or sudo apt install lm-sensors

Configure lm_sensors

sensors-detect
Enter ‘YES’ for all prompts
Check what module: cat /etc/sysconfig/lm_sensors
Load the module: modprobe (module name)

Check temperature and fan data

(in Fahrenheit): sensors -f

lm_sensors - techpain.com

lm_sensors Manual Page

Usage: sensors [OPTION]... [CHIP]...
-c, --config-file     Specify a config file (default: /etc/sensors.conf)
-h, --help            Display this help text
-s, --set             Execute `set' statements (root only)
-f, --fahrenheit      Show temperatures in degrees fahrenheit
-A, --no-adapter      Do not show adapter for each chip
-U, --no-unknown      Do not show unknown chips
-u, --unknown         Treat chips as unknown ones (testing only)
-v, --version         Display the program version Use `-' after `-c' to read the config file from stdin.
If no chips are specified, all chip info will be printed.
Example chip names:
lm78-i2c-0-2d   *-i2c-0-2d
lm78-i2c-0-*    *-i2c-0-*
lm78-i2c-*-2d   *-i2c-*-2d
lm78-i2c-*-*    *-i2c-*-*
lm78-isa-0290   *-isa-0290
lm78-isa-*      *-isa-*
lm78-*

Configure monitoring

Write a script to cron or check via Nagios/nrpe. This can be as simple or complex as you like. I like to use something like this since it checks each temp individually, and has a separate threshold for each in a single script:

#!/bin/bash

# By techpain 2012-12-11
# Check temperatures

TEMP1=$(sensors -f | grep -A3 'k8temp-pci-00c3' | grep Core0 | awk '{print $3}' | sed 's/\+//' | sed 's/.\{4\}$//')
TEMP2=$(sensors -f | grep -A3 'k8temp-pci-00c3' | grep Core1 | awk '{print $3}' | sed 's/\+//' | sed 's/.\{4\}$//')
TEMP3=$(sensors -f | grep -A3 'k8temp-pci-00cb' | grep Core0 | awk '{print $3}' | sed 's/\+//' | sed 's/.\{4\}$//')
TEMP4=$(sensors -f | grep -A3 'k8temp-pci-00cb' | grep Core1 | awk '{print $3}' | sed 's/\+//' | sed 's/.\{4\}$//')

if [ $TEMP1 -le 85 ] && [ $TEMP2 -le 75 ] && [ $TEMP3 -le 100 ] && [ $TEMP4 -le 100 ]
then
echo "OK - $TEMP1,$TEMP2,$TEMP3,$TEMP4 - cool as the other side of the pillow"
exit 0
else
logger "WARN - $TEMP1,$TEMP2,$TEMP3,$TEMP4 - it's getting hot in here"
echo "WARN - $TEMP1,$TEMP2,$TEMP3,$TEMP4 - it's getting hot in here"
exit 1
fi

lm_sensors monitoring script output - techpain.com

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df error – ‘df: cannot read table of mounted file systems’

[root@host]# df -h
df: cannot read table of mounted file systems
[root@host]# cat etc/mtab
(nothing)
[root@host]# lvdisplay
Parse error at byte 6 (line 1): unexpected token

This is often related to a disk space issue. A post from insanelabs.com recommended freeing up space and then rebuilding /etc/mtab from /proc/mounts like so:
[root@host]# grep -v rootfs /proc/mounts > /etc/mtab
Seemed to do the trick, df is now returning expected results.

df - techpain.com

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RHEL 4 – Reset root Password

Recently received a server running RHEL4 and didn’t have user credentials, let alone root access. Used the following method, taken from redhat.com:

Help! I forgot my root password. How do I log in now?

You can log in using single-user mode and create a new root password.

To enter single-user mode, reboot your computer. If you use the default boot loader, GRUB, you can enter single user mode by performing the following:

1. At the boot loader menu, use the arrow keys to highlight the installation you want to edit and type [A] to enter into append mode.

2. You are presented with a prompt that looks similar to the following:
grub append> ro root=LABEL=/

3. Press the Spacebar once to add a blank space, then add the word single to tell GRUB to boot into single-user Linux mode. The result should look like the following:
ro root=LABEL=/ single

4. Press [Enter] and GRUB will boot single-user Linux mode. After it finishes loading, you will be presented with a shell prompt similar to the following:
sh-2.05b#

5. You can now change the root password by typing
passwd root
You will be asked to re-type the password for verification. Once you are finished, the password will be changed. You can then reboot by typing reboot at the prompt; then you can log in to root as you normally would.

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