Difference between pages "Pxe" and "Snmp"

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(Difference between pages)
imported>ThorstenStaerk
 
imported>ThorstenStaerk
 
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'''PXE''' stands for '''P'''reboot E'''x'''ecution '''E'''nvironment. It is used to boot a computer using booting information from over the network.
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SNMP allows you to monitor hardware. To do this, there are objects that will be monitored: computers, network switches, storages and so on. These are called agents. They communicate with a "manager" which displays their status. The agents can be queried for their status by a get/set request/response. Or they can alert about a critical status by initiating a communication, this is called a "trap".
  
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= Overview =
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= Trying to build an SNMP prototype =
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The typical PXE boot looks like this:
 
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# Computer ''A'' starts. Its [http://en.wikipedia.org/wiki/BIOS BIOS] is set to do a PXE boot, so booting from the [[network]].
 
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# Computer ''A'' acquires an IP address from [[dhcp]] server ''B''.
 
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# Computer ''A'' downloads its booting files ([[initrd]] and kernel) via [[tftp]] from ''B''.
 
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# Computer ''A'' executes the kernel just as if it had from its local [[hard disk]].
 
  
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= How to start =
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SUSE Linux:
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In this example we use SUSE Linux 12.1.
 
  
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== DHCP ==
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yast -i nagios apache2
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To allow your computers to boot from the network, they first need an IP address. So, [[set up a dhcp-server]]. Make sure /etc/dhcpd.conf contains the following lines:
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/etc/init.d/nagios start
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allow booting;
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  /etc/init.d/apache2 start
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allow bootp;
 
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authoritative; # I am the one and only here
 
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Make sure your "subnet" section contains the following lines:
 
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next-server ''192.168.0.5'';
 
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filename "pxelinux.0";
 
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Make sure you have restarted your dhcpd:
 
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  /etc/init.d/dhcpd restart
 
  
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== TFTP ==
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Remember your login nagiosadmin:nagiosadmin and point your browser to http://127.0.0.1/nagios
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After your computers have received their IP address, they start asking for their booting file from the TFTP-server, in this case ''192.168.0.5''. So, make sure they can get it.
 
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* [[Install]] tftp and syslinux:
 
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# yast -i tftp syslinux
 
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* copy syslinux' pxelinux.0 to /srv/tftpboot/:
 
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# rpm -ql syslinux | grep pxelinux.0
 
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/usr/share/syslinux/gpxelinux.0
 
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/usr/share/syslinux/pxelinux.0
 
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# cp /usr/share/syslinux/pxelinux.0 /srv/tftpboot/
 
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* Activate the tftp server. To do this, change /etc/xinetd.d/tftp. Replace
 
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disable = yes
 
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with
 
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disable = no
 
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Then restart xinetd which hosts tftpd:
 
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/etc/init.d/xinetd restart
 
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* Test it:
 
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tftp ''192.168.0.5'' -c get pxelinux.0
 
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Test your configuration now by booting a connected computer from PXE. You should get an error message saying that the configuration file pxelinux.cfg/default has not been found.
 
  
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== pxelinux.cfg/default ==
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/etc/init.d/snmptrapd
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Create a /srv/tftpboot/pxelinux.cfg/default like this:
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tail -f /var/log/net-snmpd.log
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  default linux
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  snmptrap -v 2c -c public localhost "" NET-SNMP-EXAMPLES-MIB::netSnmpExampleHeartbeatNotification netSnmpExampleHeartbeatRate i 42
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timeout 0
 
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prompt 1
 
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display display.msg
 
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label linux
 
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  kernel vmlinuz
 
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  append initrd=initrd
 
  
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* Now you must supply kernel (vmlinuz) and initrd into the tftp folder:
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  No access configuration - dropping trap.
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  cp /boot/vmlinuz /srv/tftpboot
 
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cp /boot/initrd /srv/initrd
 
  
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== Change initial ramdisk ==
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So it seems I have to  
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If you now want to change the initrd to actually do something, you can do it like this:
 
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cd /srv/tftpboot
 
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mkdir tmp
 
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cd tmp
 
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cp ../initrd ./initrd.gz
 
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gunzip initrd.gz
 
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mkdir tmp2
 
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cd tmp2
 
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[[cpio]] -id < ../initrd
 
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Do the needed changes now in this folder. Then pack the initrd again:
 
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[[find]] . | cpio --create --format='newc' > ../newinitrd
 
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cd ..
 
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[[gzip]] newinitrd
 
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Your new [[initrd]] is now called newinitrd.gz.
 
  
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== Basic setup ==
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cat /etc/snmp/snmptrapd.conf
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The goal here is to be able to boot a Linux shell from PXE.
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disableAuthorization yes
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traphandle default /bin/snmppl
  
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For this I took the initrd and kernel from the SUSE 12.1 install DVD and modified the initrd. I replaced /init on the initrd by /bin/bash. Then I copied busybox to /bin. Then I booted from PXE. Then I mounted /proc:
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/etc/init.d/snmptrapd restart
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  mount -t proc proc /proc
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cat /bin/snmppl
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#!/bin/bash
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date >>/tmp/dates
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= 2014-05-06 =
 +
Ok, the following command
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snmptrap -v 2c -c public hostname "" NET-SNMP-EXAMPLES-MIB::netSnmpExampleHeartbeatNotification netSnmpExampleHeartbeatRate i 42
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works and I can see on hostname
 +
 
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hostname:~ # tcpdump port 162
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tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
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listening on eth0, link-type EN10MB (Ethernet), capture size 96 bytes
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12:09:02.418760 IP source.domain.45398 > hostname.domain.snmptrap:  V2Trap(77)  system.sysUpTime.0=60543145 S:1.1.4.1.0=[|snmp]
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 +
But I cannot receive it with [[netcAt]]. And it does not work on localhost.
 +
 
 +
Using this command I can sniff and display the snmp trap:
 +
 
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tcpdump -A port 162 -l | hexdump -C
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or this command:
 +
 
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  netcat -u -l 162 | hexdump -C
  
 
= See also =
 
= See also =
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* [http://en.wikipedia.org/wiki/Preboot_Execution_Environment Wikipedia on PXE]
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* http://nagios.sourceforge.net/docs/3_0/quickstart-opensuse.html
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* http://www.digitalpeer.com/id/linuxnfs
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* http://net-snmp.sourceforge.net/wiki/index.php/TUT:snmptrap
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* http://www.linuxforums.org/forum/gentoo-linux/108864-net-snmp.html
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* http://paulgporter.net/2013/09/16/nagios-snmp-traps/
  
 
[[Category:Networking]]
 
[[Category:Networking]]
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[[Category:Boot]]
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[[Category:Concept]]
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[[Category:Guides]]
 

Revision as of 10:40, 22 January 2015

SNMP allows you to monitor hardware. To do this, there are objects that will be monitored: computers, network switches, storages and so on. These are called agents. They communicate with a "manager" which displays their status. The agents can be queried for their status by a get/set request/response. Or they can alert about a critical status by initiating a communication, this is called a "trap".

Trying to build an SNMP prototype

SUSE Linux: 

yast -i nagios apache2
/etc/init.d/nagios start
/etc/init.d/apache2 start

Remember your login nagiosadmin:nagiosadmin and point your browser to http://127.0.0.1/nagios 

/etc/init.d/snmptrapd
tail -f /var/log/net-snmpd.log
snmptrap -v 2c -c public localhost "" NET-SNMP-EXAMPLES-MIB::netSnmpExampleHeartbeatNotification netSnmpExampleHeartbeatRate i 42

No access configuration - dropping trap.

So it seems I have to 

cat /etc/snmp/snmptrapd.conf
disableAuthorization yes
traphandle default /bin/snmppl

/etc/init.d/snmptrapd restart
cat /bin/snmppl
#!/bin/bash
date >>/tmp/dates

2014-05-06

Ok, the following command 

snmptrap -v 2c -c public hostname "" NET-SNMP-EXAMPLES-MIB::netSnmpExampleHeartbeatNotification netSnmpExampleHeartbeatRate i 42

works and I can see on hostname 

hostname:~ # tcpdump port 162
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on eth0, link-type EN10MB (Ethernet), capture size 96 bytes
12:09:02.418760 IP source.domain.45398 > hostname.domain.snmptrap:  V2Trap(77)  system.sysUpTime.0=60543145 S:1.1.4.1.0=[|snmp]

But I cannot receive it with netcAt. And it does not work on localhost.

Using this command I can sniff and display the snmp trap: 

tcpdump -A port 162 -l | hexdump -C

or this command: 

netcat -u -l 162 | hexdump -C

See also

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