Lightning talk for an intro to Augeas at OggCamp 12. Briefly explains the library, examples of what it can do and where it's used. Based on a presentation by Raphaël Pinson (search for RMLL 2012).

1. Configuration surgery
with Augeas
Dominic Cleal
dcleal@redhat.com
OggCamp 12, Liverpool
19th August 2012
Presentation forked from Raphaël Pinson's at RMLL 2012

2. Tired of ugly sed and awk one liners?
or of using tons of different parsing libraries or
brittle tricks?
OggCamp | 2 | Dominic Cleal

3. Become a configuration surgeon with
Augeas
OggCamp | 3 | Dominic Cleal

4. What is the need?
● Many different syntaxes
● Securely editing configuration files with a
unified API
OggCamp | 4 | Dominic Cleal

5. A tree, its branches and leaves
Augeas turns configuration files into a tree
structure:
/etc/hosts -> /files/etc/hosts
... and their parameters into branches and
leaves:
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"
OggCamp | 5 | Dominic Cleal

6. Augeas provides many stock parsers
They are called lenses:
Access Cron Host_Conf
Aliases Crypttab Hostname
Anacron debctrl Hosts_Access
Approx Desktop IniFile
AptConf Dhcpd Inputrc
Automaster Dpkg Iptables
Automounter Exports Kdump
BackupPCHosts FAI_DiskConfig Keepalived
cgconfig Fonts Keepalived
cgrules Fuse Login_defs
Channels Grub Mke2fs
...
$ augtool print /augeas//path | wc -l
788
OggCamp | 6 | Dominic Cleal

7. augtool lets you inspect the tree
$ augtool
augtool> ls /
augeas/ = (none)
files/ = (none)
augtool> print /files/etc/passwd/root/
/files/etc/passwd/root
/files/etc/passwd/root/password = "x"
/files/etc/passwd/root/uid = "0"
/files/etc/passwd/root/gid = "0"
/files/etc/passwd/root/name = "root"
/files/etc/passwd/root/home = "/root"
/files/etc/passwd/root/shell = "/bin/bash"
OggCamp | 7 | Dominic Cleal

8. The tree can be queried using XPath
augtool> print /files/etc/passwd/*[uid='0'][1]
/files/etc/passwd/root
/files/etc/passwd/root/password = "x"
/files/etc/passwd/root/uid = "0"
/files/etc/passwd/root/gid = "0"
/files/etc/passwd/root/name = "root"
/files/etc/passwd/root/home = "/root"
/files/etc/passwd/root/shell = "/bin/bash"
OggCamp | 8 | Dominic Cleal

9. But also modified
$ grep root /etc/fstab
/dev/mapper/vgiridium-lvroot / ext4 defaults 1 1
$ augtool
augtool> match /files/etc/fstab/*[file='/']/opt
/files/etc/fstab/1/opt = defaults
augtool> set /files/etc/fstab/*[file='/']/opt noatime
augtool> match /files/etc/fstab/*[file='/']/opt
/files/etc/fstab/1/opt = noatime
augtool> save
Saved 1 file(s)
augtool> exit
$ grep root /etc/fstab
/dev/mapper/vgiridium-lvroot / ext4 noatime 1 1
OggCamp | 9 | Dominic Cleal

10. Bindings include Perl, Python, Java, PHP, Ruby...
...OCaml, Haskell, Lua, Vala...
#!/usr/bin/env ruby
require 'augeas'
aug = Augeas.open
# Print each mount
aug.match("/files/etc/fstab/*[file]").each do |m|
mount = aug.get("#{m}/file")
dev = aug.get("#{m}/spec")
puts "#{dev} is mounted at #{mount}"
end
# Edit / mount option
aug.set("/files/etc/fstab/*[file='/']/opt",
"noatime")
aug.save!
OggCamp | 10 | Dominic Cleal

11. Puppet has a native provider
augeas { 'export /foo':
context => '/files/etc/exports',
changes => [
"set dir[. = '/foo'] /foo",
"set dir[. = '/foo']/client weeble",
"set dir[. = '/foo']/client/option[1] ro",
"set dir[. = '/foo']/client/option[2] all_squash",
],
}
$ cat /etc/exports
/foo weeble(ro,all_squash)
OggCamp | 11 | Dominic Cleal

12. Other projects using Augeas
● libguestfs
● virt-tools, e.g. p2v, v2v
● NUT
● ZYpp
● Config::Model
● Augeas::Validator
OggCamp | 13 | Dominic Cleal

13. Questions?
http://augeas.net
augeas-devel@redhat.com
freenode: #augeas
OggCamp | 14 | Dominic Cleal