Skip to main content

Extending SNMP to run arbitrary shell script

Why are we here...

This is not likely something I would have pursued under normal circumstances.  I happen to be working for a customer/client who is not afforded a lot of flexibility to accomplish their goals.  In this case, the rigor is justified.  They have to sometimes be fairly creative with how they solve problems.

In this case they would like to utilize an existing snmp implementation to execute a command (or shell script) on a remote system.  They came to me with the idea of using Net-SNMP extend.
https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/6/html/Deployment_Guide/sect-System_Monitoring_Tools-Net-SNMP-Extending.html

NOTE:  This is NOT a good implementation strategy in the "real world"  it will simply allow you to test the functionality.  There are a TON of security implications which would need to be taken in to consideration.

Implementation Steps:

[root@rh7tst01 ~]# yum -y install net-snmp net-snmp-utils
[root@rh7tst01 ~]# cd /etc/snmp
[root@rh7tst01 snmp]# grep -v \# snmpd.conf | grep -v ^$
com2sec notConfigUser  default       public
group   notConfigGroup v1           notConfigUser
group   notConfigGroup v2c           notConfigUser
view    systemview    included   .1.3.6.1.2.1.1
view    systemview    included   .1.3.6.1.2.1.25.1.1
view    systemview included   .1
access  notConfigGroup ""      any       noauth    exact  systemview none none
syslocation Unknown (edit /etc/snmp/snmpd.conf)
syscontact Root <root@localhost> (configure /etc/snmp/snmp.local.conf)
dontLogTCPWrappersConnects yes

-- Update/create snmpd.local.conf
[root@rh7tst01 snmp]# grep -v \# snmpd.local.conf
syscontact James Radtke <root@localhost>
syslocation Laptop, Virtual Machine

extend sshd_pids /usr/local/bin/check_proc.sh sshd

-- Restart and enable snmpd
[root@rh7tst01 snmp]# systemctl restart snmpd
[root@rh7tst01 snmp]# systemctl enable $_

-- Update the firewall
[root@rh7tst01 snmp]# firewall-cmd --permanent --add-port=161/udp
[root@rh7tst01 snmp]# firewall-cmd --reload
[root@rh7tst01 snmp]# cat /usr/local/bin/check_procs.sh
#!/bin/sh

 PATTERN=$1
NUMPIDS=`pgrep $PATTERN | wc -l`

 echo "There are $NUMPIDS $PATTERN processes."
exit $NUMPIDS


Test your config

[root@rh7tst01 snmp]# snmpwalk -v 2c -c public localhost NET-SNMP-EXTEND-MIB::nsExtendObjects
NET-SNMP-EXTEND-MIB::nsExtendNumEntries.0 = INTEGER: 1
NET-SNMP-EXTEND-MIB::nsExtendCommand."sshd_pids" = STRING: /usr/local/bin/check_proc.sh
NET-SNMP-EXTEND-MIB::nsExtendArgs."sshd_pids" = STRING: sshd
NET-SNMP-EXTEND-MIB::nsExtendInput."sshd_pids" = STRING: 
NET-SNMP-EXTEND-MIB::nsExtendCacheTime."sshd_pids" = INTEGER: 5
NET-SNMP-EXTEND-MIB::nsExtendExecType."sshd_pids" = INTEGER: exec(1)
NET-SNMP-EXTEND-MIB::nsExtendRunType."sshd_pids" = INTEGER: run-on-read(1)
NET-SNMP-EXTEND-MIB::nsExtendStorage."sshd_pids" = INTEGER: permanent(4)
NET-SNMP-EXTEND-MIB::nsExtendStatus."sshd_pids" = INTEGER: active(1)
NET-SNMP-EXTEND-MIB::nsExtendOutput1Line."sshd_pids" = STRING: There are 2 sshd processes.
NET-SNMP-EXTEND-MIB::nsExtendOutputFull."sshd_pids" = STRING: There are 2 sshd processes.
NET-SNMP-EXTEND-MIB::nsExtendOutNumLines."sshd_pids" = INTEGER: 1
NET-SNMP-EXTEND-MIB::nsExtendResult."sshd_pids" = INTEGER: 2
NET-SNMP-EXTEND-MIB::nsExtendOutLine."sshd_pids".1 = STRING: There are 2 sshd processes.

-- Now, figure out the OID location
[root@rh7tst01 ~]# snmptranslate -On NET-SNMP-EXTEND-MIB::nsExtendOutLine
.1.3.6.1.4.1.8072.1.3.2.4.1.2

-- Poll the OID
[root@rh7tst01 ~]# snmpwalk -v 2c -c public localhost .1.3.6.1.4.1.8072.1.3.2.4.1.2
NET-SNMP-EXTEND-MIB::nsExtendOutLine."sshd_pids".1 = STRING: There are 4 sshd processes.

SNMP Foo

Review the man pages for the following helpful commands:
snmpd -H
snmpd -V -c /etc/snmp/snmpd.conf
snmpconf -g basic_setup




References:

https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/6/html/Deployment_Guide/sect-System_Monitoring_Tools-Net-SNMP-Extending.html
http://www.net-snmp.org/docs/mibs/NET-SNMP-EXTEND-MIB.txt
Labels:

Comments

Post a Comment

Popular posts from this blog

PXE boot a LiveCD image

Summary: I have wanted to build a kickstart environment which hosted a "rescue CD" or LiveCD to allow you to boot over the network after you blew your stuff up and needed to repair a few things.  Today I have worked through a method of doing so, with the help of the people who published a succinct script with the Red Hat Enterprise Virtualization Hypervisor.  (the script will be at the bottom of this post - if I have somehow not followed the GPL, please let me know and I will correct whatever is necessary) NOTE/Warning: The boot will fail due the initrd being too large (645mb).  I'm not sure how to proceed.  This procedure worked for RHEVh, because it is quite a bit smaller.  Hopefully I can report back with progress on this? :-$ Procedure: download your LiveCD image to /export/isos/RESCUE/Fedora-16-i686-Live-Desktop.iso # cd /var/tmp # vi livecd-iso-to-pxeboot (populate the file with the script shown below) # chmod 754 ./livecd-iso-to-pxeb...
2 comments
Read more

"Error getting authority: Error initializing authority: Could not connect: No such file or directory (g-io-error-quark, 1)"

"Error getting authority: Error initializing authority: Could not connect: No such file or directory (g-io-error-quark, 1)" One issue that may cause this to arise is if you managed to break your /etc/fstab We had an engineer add a line with the intended options of "nfsvers=3" but instead added "-onfsvers=3" and it broke the system fairly catastrophically.
Post a Comment
Read more

MOTD with colors! (also applies to shell profiles)

I'm not sure why I had never looked into this before, but this evening I became obsessed with discovering how to present different colored text in the /etc/motd. A person had suggested creating a shell script (rather than using special editing modes in vi, or something) and I agree that is the simplest way of getting this accomplished quickly. This most noteworthy portion of this script is the following: RESET="\033[0m" that puts the users shell back to the original color. I typically like a green text on black background. Also - a great reference for the different colors and font-type (underscore, etc...) https://wiki.archlinux.org/index.php/Color_Bash_Prompt I found this example on the web and I wish I could recall where so that I could provide credit to that person. #!/bin/bash #define the filename to use as output motd="/etc/motd" # Collect useful information about your system # $USER is automatically defined HOSTNAME=`uname -n` KERNEL=`un...
1 comment
Read more