So far we have covered how to ensure the content of a whole file, by using static sample-files which are housed in a puppet module#s “files” folder, or by using .erb files which are stored in the module’s “templates” folder.
AnnouncementYou can find all my latest posts on medium.
However there will be times when you don’t want to ensure the content of the whole file, instead you just want to ensure the content of part of a file. For example you may just want to add a line to the /etc/hosts file.
This is especially the case when dealing with config files that are part of the OS. For example /etc/hosts and /etc/fstab. Other Sys admins may make manual changes to these files. so if you ensure the state of this file using static-files/templates, then it will end up constantly over-riding manual changes made by the system administrators.
Hence the need to ensure a file’s state at a more granular line/section level rather than at a file level.
Controlling the state of a certain line or (group of lines) is present in a given file is possible in puppet thanks to the augeas resource type.
Augeas is actually a standalone tool, and you can use it completely seperately from Puppet. However Augeas is so powerful and useful, that Puppetlabs decided to develop the Augeas resource type in order for puppet to natively support it.
Using Augeas on it’s own
For the time being let’s forget about Puppet, and just look at Augeas on it’s own.
To begin with, you first need to install augeas:
yum install augeas
The main Augeas standalone tool is a commandline shell, called “augtool”:
[root@puppetmaster /]# rpm -ql augeas /usr/bin/augparse /usr/bin/augtool /usr/bin/fadot /usr/share/man/man1/augparse.1.gz /usr/share/man/man1/augtool.1.gz /usr/share/vim/vimfiles/ftdetect/augeas.vim /usr/share/vim/vimfiles/syntax/augeas.vim [root@puppetmaster augeas]#
Hence to start a new augtool, we do:
[root@puppetmaster /]# augtool augtool>
You can exit the augtool terminal using the quit command.
[root@puppetmaster /]# augtool augtool>
Use the “help” command to see what other commands are available under augtool:
[root@puppetmaster /]# augtool augtool> help Admin commands: help - print help load - (re)load files under /files quit - exit the program retrieve - transform tree into text save - save all pending changes store - parse text into tree transform - add a file transform Read commands: dump-xml - print a subtree as XML get - get the value of a node label - get the label of a node ls - list children of a node match - print matches for a path expression print - print a subtree span - print position in input file corresponding to tree Write commands: clear - clear the value of a node clearm - clear the value of multiple nodes ins - insert new node insert - insert new node (alias of 'ins') mv - move a subtree move - move a subtree (alias of 'mv') rename - rename a subtree label rm - delete nodes and subtrees set - set the value of a node setm - set the value of multiple nodes touch - create a new node Path expression commands: defnode - set a variable, possibly creating a new node defvar - set a variable Type 'help
' for more information on a command augtool>
The augeas tool view files in the form of an object. It can view this object in the form of a hierarchial tree structure.
Augeas (aka augtool) is used for querying and editing config files from the command line. Augtool lets you navigate/drill-down to a particular part of a config file.
In our guide, we will use the /etc/hosts file as an example. In our example, the hosts file currently contains:
[root@puppetmaster /]# cat /etc/hosts 127.0.0.1 localhost 127.0.1.1 puppetmaster.sherc.sg-host.com puppetmaster 10.1.172.10 puppetmaster.sherc.sg-host.com puppet puppetmaster 10.1.172.11 puppetagent01.sherc.sg-host.com puppetagent01 10.1.172.12 puppetagent02.sherc.sg-host.com puppetagent02 10.1.172.13 puppetagent03.sherc.sg-host.com puppetagent03 [root@puppetmaster /]#
Note, as you can see above, we have 6 entries.
However augeas cannot query/edit any config file, but only those that it is has a schema (aka lens) for. There are a set of stock lenses that comes with augeas by default. These lens are stored in:
[root@puppetmaster dist]# pwd /usr/share/augeas/lenses/dist [root@puppetmaster dist]# ls -l total 840 -rw-r--r-- 1 root root 3550 Nov 2 2012 access.aug -rw-r--r-- 1 root root 1485 Feb 10 10:51 activemq_conf.aug -rw-r--r-- 1 root root 841 Feb 10 10:51 activemq_xml.aug -rw-r--r-- 1 root root 2231 Nov 2 2012 aliases.aug -rw-r--r-- 1 root root 2564 Nov 2 2012 anacron.aug . . . ...etc [root@puppetmaster dist]#
Let’s just take at the hosts.aug lens file:
[root@puppetmaster dist]# cat hosts.aug (* Parsing /etc/hosts *) module Hosts = autoload xfm let sep_tab = Util.del_ws_tab let sep_spc = Util.del_ws_spc let eol = Util.eol let indent = Util.indent let comment = Util.comment let comment_or_eol = Util.comment_or_eol let empty = [ del /[ \t]*#?[ \t]*\n/ "\n" ] let word = /[^# \n\t]+/ let record = [ seq "host" . indent . [ label "ipaddr" . store word ] . sep_tab . [ label "canonical" . store word ] . [ label "alias" . sep_spc . store word ]* . comment_or_eol ] let lns = ( empty | comment | record ) * let xfm = transform lns (incl "/etc/hosts") [root@puppetmaster dist]#
Don’t worry too much about what all this means, but notice that there are 3 labels defined here, “ipaddr”, “canonical”, and “alias”. These labels are used to label different parts of a config file’s line/section.
Now let’s take a look at how to query values in the /etc/hosts file:
To do this we use the augtool’s “ls” command.
The “ls” command actually let’s you navigate to a particular file you want to change, and then lets you drill down further to a particular line of that file:
[root@puppetmaster /]# augtool augtool> ls / augeas/ = (none) files/ = (none)
Now since we want to query a file, we drill down into files:
augtool> ls /files etc/ = (none) boot/ = (none) augtool>
Since the hosts file resides in /etc folder, we now go there:
augtool> ls /files/etc/ puppet/ = (none) hosts/ = (none) # this is the one we are interested in. . . . ....etc augtool>
Notice that the “hosts/” appears as a directory. That’s augeas way of telling us that we can drill down further into the file itself.
Now let’s drill down into hosts file:
[root@puppetmaster /]# cat /etc/hosts augtool> ls /files/etc/hosts 1/ = (none) 2/ = (none) 3/ = (none) 4/ = (none) 5/ = (none) 6/ = (none) augtool>
The 1-6 entries matches up with the lines in the /etc/hosts file that we saw earlier.
Now we can pick a line to drill down to a particular line, e.g. let’s pick line 3:
augtool> ls /files/etc/hosts/3 ipaddr = 10.1.172.10 canonical = puppetmaster.sherc.sg-host.com alias = puppet alias = puppetmaster augtool>
At this point we have drilled down to a particular node, and hence we now see labels along with the value it houses. We can now use the “get” command to display a particular label’s value:
augtool> get /files/etc/hosts/3/ipaddr /files/etc/hosts/3/ipaddr = 10.1.172.10 augtool>
We can now edit this value using the set command, e.g. let’s change it from “10.1.172.10” to “126.96.36.199”. We do this using the “set” command:
augtool> set /files/etc/hosts/3/ipaddr 188.8.131.52 augtool> get /files/etc/hosts/3/ipaddr /files/etc/hosts/3/ipaddr = 184.108.40.206 augtool> ls /files/etc/hosts/3 ipaddr = 220.127.116.11 canonical = puppetmaster.sherc.sg-host.com alias = puppet alias = puppetmaster augtool>
Now that we have checked the change, and are happy with it, we can then save it and exit:
augtool> save Saved 1 file(s) augtool> quit [root@puppetmaster /]#
Now if we check the content of the /etc/hosts file:
[root@puppetmaster /]# cat /etc/hosts 127.0.0.1 localhost 127.0.1.1 puppetmaster.sherc.sg-host.com puppetmaster 18.104.22.168 puppetmaster.sherc.sg-host.com puppet puppetmaster 10.1.172.11 puppetagent01.sherc.sg-host.com puppetagent01 10.1.172.12 puppetagent02.sherc.sg-host.com puppetagent02 10.1.172.13 puppetagent03.sherc.sg-host.com puppetagent03 [root@puppetmaster /]#
As you can see the 3 config item’s ip address has now been changed to 22.214.171.124.
In this example, we just edited an existing line. You can also append a new line, delete lines, insert lines….etc.
Another useful command is the print command. This let’s you view a file in the form of an object:
augtool> print /files/etc/hosts /files/etc/hosts /files/etc/hosts/1 /files/etc/hosts/1/ipaddr = "127.0.0.1" /files/etc/hosts/1/canonical = "localhost\r" /files/etc/hosts/2 /files/etc/hosts/2/ipaddr = "127.0.1.1" /files/etc/hosts/2/canonical = "puppetmaster.sherc.sg-host.com" /files/etc/hosts/2/alias = "puppetmaster\r" /files/etc/hosts/3 /files/etc/hosts/3/ipaddr = "10.1.172.10" /files/etc/hosts/3/canonical = "puppetmaster.sherc.sg-host.com" /files/etc/hosts/3/alias = "puppet" /files/etc/hosts/3/alias = "puppetmaster\r" /files/etc/hosts/4 /files/etc/hosts/4/ipaddr = "10.1.172.11" /files/etc/hosts/4/canonical = "puppetagent01.sherc.sg-host.com" /files/etc/hosts/4/alias = "puppetagent01\r" /files/etc/hosts/5 /files/etc/hosts/5/ipaddr = "10.1.172.12" /files/etc/hosts/5/canonical = "puppetagent02.sherc.sg-host.com" /files/etc/hosts/5/alias = "puppetagent02\r" /files/etc/hosts/6 /files/etc/hosts/6/ipaddr = "10.1.172.13" /files/etc/hosts/6/canonical = "puppetagent03.sherc.sg-host.com" /files/etc/hosts/6/alias = "puppetagent03\r"