Unix System Administration

Chuck Hauser2007-10-19

Cfengine

Automated suite of programs for configuring and maintaining Unix-like computers

Developed by Mark Burgess of Oslo University College

Started in 1993; wanted to replace shell scripts with a declarative language that documented configurations.

Some Cfengine Capabilities

Check or set file ownership and permissions

Edit configuration files Remove unwanted files (“tidy”) Check integrity of important files Process management

Implementing Cfengine

Primary Documentation: www.cfengine.org Secondary Documentation: Wikipedia lists

several Cfengine links Software: required packages are at

www.sunfreeware.com

Additional Useful Info

Luke A. Kanies: Introducing Cfenginehttp://www.onlamp.com/pub/a/onlamp/2004/04/15/cfengine.html

Chapter 6 from Kirk Bauer: Automating UNIX and Linux Administration

http://www.apress.com/book/downloadfile/1169

AEleen Frisch: Top Five Open Source Packages for System Administrators

http://www.onlamp.com/pub/a/onlamp/2003/05/29/essentialsysadmin.html

System configuration with CFEngine http://sial.org/howto/cfengine/

Mark Burgess and AEleen Frisch: A System Engineer’s Guide to Host Configuration and Maintenance Using Cfengine

http://www.sage.org

Cfengine Software Packages

Follow the required packages list on Sunfreeware.com. File names consist of package-version-os_version-architecture-default_directory; e.g. cfengine-2.1.20-sol9-sparc-local.gz.

Cfengine GNU cfengine program suite

libgcc GCC libraries

db Berkley embedded database

openssl SSL/TSL cryptography library

Installing Packages Put packages in /var/spool/pkg. Install in this order: libgcc, db, openssl,

cfengine. Unzip each package:# gunziplibgcc-3.3-sol9-sparc-local.gz

Then install as root: # pkgadd –dlibgcc-3.3-sol9-sparc-local

Cfengine Directory Structure

After package installation, libraries are in /usr/local/lib and binaries are in /usr/local/sbin.

Cfengine’s production location is /var/cfengine: /var/cfengine/bin stores programs, ./inputs stores configuration files, and ./outputs stores output from cfagent runs in timestamped files.

Additional /var/cfengine directories are created as needed by the Cfengine programs.

Setup Script for Cfengine#!/usr/bin/ksh#if [ ! -f /usr/local/sbin/cfagent ]then echo "Quitting, no cfengine programs on this machine!" exitfi

if [ ! -d /var/cfengine/bin ]then mkdir -p /var/cfengine/bin chown root:other /var/cfengine/binfi

Setup Script continuedcd /usr/local/sbincp cfagent cfenvgraph cfrun cfdoc cfexecd \ cfservd cfenvd cfkey cfshow vicf \

/var/cfengine/bin

if [ ! -d /var/cfengine/inputs ]then mkdir /var/cfengine/inputsfi

if [ ! -d /var/cfengine/outputs ]then mkdir /var/cfengine/outputsfi

Some Cfengine Programs

cfagentThe configuration agent; implements a machine’s configuration

cfkeyGenerates public/private key pairs; usually run only once.

cfexecdExecute and reporting daemon (for cfagent).

cfservdFor file transfer and remote execution (runs on a central configuration server)

cfrunRun from server; contacts cfservd to run cfagent (rarely used)

How It Works

A configuration file describes the state a system should be in

Descriptive, not procedural; does not describe explicitly how to achieve that state

A single cfengine run may result in multiple passes (“convergence”)

Single host setup only requires the cfagent program and a cfagent.conf file that describes the desired configuration

The Configuration File A configuration file consists of actions and

classes (also called groups) Actions either tell the program how to behave or

what to do. Actions are often followed by statements in this

form: name = ( list ) Classes may be used to restrict a particular

action to a host that is only a member of that class (group)

May have variables: these may be special internal variables, user-defined strings, or shell environment variables

Configuration File Structure

File consists of action sections, which are reserved words followed by a colon

Some sections are for initial settings and definitions: acl, alerts, binservers, broadcast, control, defaultroute, filters, groups, homeservers, ignore, import, strategies, etc.

Other sections perform specific actions: alerts, copy, disks, disable, editfiles, files, links, netconfig, resolve, packages, processes, shellcommands, and tidy

It is not necessary to have or use all sections

A cfagent.conf Section

links:

easyspooler_fix::

/usr/bin/lp -> /usr/bin/llpsyslog=trueinform=true

Actions end with a colon and start a section

Classes within an action end with a double-colon

A Very Simple Configuration File# cfagent.hellocontrol:

actionsequence = ( shellcommands )

shellcommands:

“/bin/echo Hello world!”useshell=false

To execute:# /var/cfengine/bin/cfagent –f cfagent.hellocfengine:cis:/bin/echo Hello: Hello world!

Action Sequence Types 1

alerts Display messages

copyCopy files to or update files on the local system; source files can be local or remote

disksVerify presence of or free space on disk partitions

disableDeactivate system features by renaming configuration files; can also perform log rotation

Action Sequence Types 2

editfiles Modify test in configuration files

files Verify or correct file attributes

links Verify/create/correct symbolic links

netconfig Configure the network interfaces

resolveSpecify name servers etc. in resolv.conf

Action Sequence Types 3

packagesVerify presence of or install packages

processes Monitor and manage processes

shellcommandsExecute external shell commands

tidyDelete unwanted files and directories

Classes (Groups)

Classes may be predefined (also referred to as “fixed” or “hard” classes) or defined in the configuration file

Custom classes are usually defined in the groups section

“Feedback classes:” a class may also be defined using the define statement when actions are performed in other sections (for example, when disable actions are performed):define=boot_server_disabled

Predefined Classes

Operating systems: sunos_5_8, sunos_5_9 Architecture or hardware:

sparc, SUNW_Sun_Fire_480R Host name or IP address: cis, 10_1_12_23 Date and time stuff: Yr2007, March, Day12,

Monday, Hr00, Min45 Time intervals in minutes or quarter hours:

Min00-05, Min05-10, Q1, Q3, HR00_Q1

Custom Classes

Can use explicit host name:no_samba = ( cis entityclient )

Use command that returns true/false:easyspooler_fix = ( `/usr/bin/test –x /usr/bin/llp-a ! –L /usr/bin/lp` )

Use built-in functions:easyspooler =( FileExists(/usr/bin/llp) )

Built-in Functions for Classes

Several built-in functions are available for class evaluation, including:

IsNewerThan(f1,f2)True if f2 was modified more recently than f1

FileExists(file) True if file exists

IsDir(dir) True if dir is a directory

IsLink(file) True if file is a symbolic link

Built-in functions execute more quickly than using the test command.

Using Compound Classes Dot (.) is a logical AND: nfs.sunos_5_8:: Later cfengine versions also support ‘&’ for

logical AND Vertical bar (|) is a logical Or: Hr00|Hr12:: Exclamation point (!) is logical NOT: !Hr00:: Parentheses override order: dbservers.(sunos_5_8|sunos_5_9)::

Precedence is () – NOT – AND – OR

Additional Class Info The any class is a generic all-inclusive

group (same as not specifying a class) To find all defined classes using the

default configuration file: /var/cfengine/bin/cfagent –p –v

To find all defined classes using a configuration file other than cfagent.conf:/var/cfengine/bin/cfagent –p –v –f cfagent.test

Sample groups Sectiongroups:

datatel = ( IsDir(/datatel) )

# Perform MD5 checksumming on these systems do_checksum = ( cis )

# Defines an EasySpooler system that needs # to have the EasySpooler llp binary used # instead of the default lp command. easyspooler_fix = ( `/usr/bin/test

-x /usr/bin/llp -a ! -L /usr/bin/lp` )

Sample groups Section continued

# Place machines in edit_password_defaults# to edit /etc/default/passwd fileedit_password_defaults = ( cis entityclient )

# If at.allow or cron.allow exist, don't need# the .deny filesno_atdeny =

( IsFile(/etc/cron.d/at.allow) )no_crondeny =

( IsFile(/etc/cron.d/cron.allow) )

Control Section

A configuration file must have a control section, otherwise nothing will be done

Sets default variables Can also be used to define new variables Defines which actions are carried out and

in what order

Cfengine Variables

Used for string substitution, similar to a macro processor

Can be defined in the control section for use in other sections:datatel_age_hold = ( 30 )

May be defined within a specific group, but this must be used carefully – some must be defined globally to avoid runtime errors in the tidy section.

Using Variables

Variables are dereferenced either using curly braces or parentheses preceded by a dollar sign: exclude=${unidata_log_files}

$(unidata_mnt)/bin

Using undefined variables causes syntax errors.

Control: Default Variables

The control section can be used to set numerous variables that control execution

Use access to list who can run cfengine:access = ( root )

Syslog activates syslog logging when an inform statement is encountered:syslog = ( on )

Defining Variablescontrol:

cfengine_note =( "# Note: this file managed under cfengine" )

datatel::

unidata_mnt = ( /usr/ud71 ) datatel_owner = ( datatel ) # Database locations datatel_production =

( /datatel/coll18/production )

List Variables

Variables may consist of multiple items separated by a colon:

datatel_hold_dirs =( ${datatel_production}/apphome/_HOLD_:${datatel_development}/apphome/_HOLD_:${datatel_test}/apphome/_HOLD_ )

unidata_log_files =( ${unidata_mnt}/bin/udt.errlog:${unidata_mnt}/bin/udtlatch.log:${unidata_mnt}/bin/saved_logs/udtlatch.log )

Control Section: actionsequence

The actionsequence variable specifies which actions are carried out and in what order:actionsequence = ( disable links )

Action sections in the configuration file that are not included in the actionsequence list are not performed

actionsequence continued

Classes may be used for control in the actionsequence statement:

actionsequence = (tidy.Hr03disablelinks.ThisClasseditfileslinks.ThatClass

)

The import Section

The import section is used for reading additional configuration files:

import:piopen::

cf.app_piopen

For breaking large configuration files into smaller files or for using separate files for special processing

Inheritance and import Files

The main (or parent) file is completely parsed before the import file is read

Variables and groups in the parent file are inherited in the imported file, but variables and groups in the imported file are not visible in the parent file

The disable Section

Cfengine will disable files (and directories) by renaming them instead of deleting them (as opposed to the tidy action).

If no destination name is specified, the file will be renamed by appending the suffix .cfdisabled to the file name.

disable can also be used to rotate files such as logs.

disable syntax

disable:class::

/filenamedest=filenamedefine=classlistsyslog=true/on/false/offinform=true/on/false/offaction=disable/warn…

A disable Exampledisable:

easyspooler_fix:: /usr/bin/lp syslog=true inform=true

no_boot_server.(sunos_5_8|sunos_5_9):: # Don't run boot services /etc/rc3.d/S16boot.server dest=cfdisabled.S16boot.server define=boot_server_disabled syslog=true

Feedback class

The editfiles Section Performs line-based editing on text files (or

limited binary editing) after making a backup of the file to be edited

Supports simple regular-expressions Syntax different from other actions:

editfiles:class::

{ file-to-be-editedaction “quoted-string…”

}

Sample editfiles Sectioneditfiles:

sunos_5_8|sunos_5_9::

# IIPS Baseline 4.5 # Set TCP initial sequence number # generation to RFC 1948 # unique-per-connection-ID { /etc/default/inetinit ReplaceAll "TCP_STRONG_ISS=[01]“

With "TCP_STRONG_ISS=2" }

Sample editfiles Section continued

# IIPS Baseline 5.1# Enable TCP connection tracing by inetd# (this is independent of any TCP Wrappers# logging).{ /etc/default/inetd PrependIfNoSuchLine "$(cfengine_note)" UnCommentLinesContaining "LOGGING=" ReplaceAll "LOGGING=NO“

With "LOGGING=YES" DefineClasses "modified_inetd_conf"}

The filters Section

The filters section does not perform actions, instead it is used for defining selection criteria that may be used in the files or processes sections.

filters:

{ root_owned_files Owner: "root" Result: "Owner" }

The files section

The files section can be used for File creation Checking the existence, ownership, and

permssions of files Changing the ownership and permissions

of files Testing for setuid root programs

Syntax for files

files: classes:: /file-object

mode=modeowner=uid-listgroup=gid-listaction=fixall/other-options/warnalllinks=false/stop/traverse/follow/tidyignore=patterninclude=patternexclude=pattern…

Correcting File Permissionsfiles:

datatel::

${datatel_production}/apphome mode=o+rw,g+rw,o-rwx owner=datatel group=users action=fixall ignore=_HOLD_ ignore=_PH_ ignore=BP recurse=inf

Sample report of correcting file permissionsChecking file(s) in

/datatel/coll18/production/apphomecfengine:cis: Owner of

/datatel/coll18/production/apphome/DATA/DATA_P/PAYROLL.EXPORTS/200710MO was 1010, setting to 100

cfengine:cis: Owner of /datatel/coll18/production/apphome/DATA/DATA_P/PAYROLL.EXPORTS/200710PT was 1010, setting to 100

cfengine:cis: Owner of /datatel/coll18/production/apphome/DATA/DATA_X/XCSD.DIRECTORY/DCA*804*071*14536.SEQ was 1006, setting to 100

Creating Files

# IIPS Baseline 6.5# Make sure the machine tracks# failed login attempts/var/adm/loginlog

owner=root group=sys

mode=600action=create

File Monitoring

Cfengine provides a file monitoring facility similar to the Tripwire program.

Any file flagged for file monitoring in the files section will have its md5 checksum registered in a checksums database.

On subsequent cfengine passes the file will have its md5 checksum computed and compared with the previously stored value; a warning will be issued if the values do not match.

Configuring File Monitoring

A file that stores the checksums must be defined in the control section: CheckSumDatabase = ( /var/cfengine/checksum.db )

Any files specified in the files section with the statement checksum=md5 will be monitored:

${unidata_mnt}/bin/udt_signalchecksum=md5inform=true

File Monitoring Examplefiles:(sunos_5_8|sunos_5_9)::

/sbin/* checksum=md5 action=warnall /usr/bin checksum=md5 action=warnall include=cancel include=login … include=passwd include=su

Controlling Updates To The Checksum Database

The control section’s ChecksumUpdates variable controls updating the stored checksums

The default value of no means the database will not be updated when a file’s checksum changes.

If ChecksumUpdates is set to yes, when a file’s checksum changes a warning is issued once and then the new checksum is stored in the database.

Maintaining the Checksum Database

If a patch cluster has been installed, switch ChecksumUpdates to yes to store the checksums of new binaries in the database, then return ChecksumUpdates to off.

Periodically set the CheckumPurge variable to on to remove files that no longer exist from the checksum database.

The cfengine.hostname.log

As cfagent searches file systems, it builds a log file of all root-owned setuid and setgid programs that are found.

This log is stored in /var/cfengine; the file name consists of the string ‘cfengine.’, the system’s hostname, and the suffix ‘.log’ – e.g. cfengine.cis.log.

Cfagent issues warnings on subsequent searches if a new root-owned setuid/setgid program is found that is not in the log file.

The links Section

Used to either check or create links:linkname -> object_to_link_to

Symbolic links are the default unless type=hard is specfied.

If the link exists but points to a different object, a warning is issued

If the link is specified using the ‘!’ operator (linkname ->! object_to_link_to), an existing link that points incorrectly is changed to point to the correct object.

The tidy SectionThe tidy action removes (deletes) files from the system

tidy:/directory

pattern/include=wildcardignore=patternexclude=patternage=dayssyslog=true/on/false/offinform=/true/on/false/off

A tidy Example

tidy:datatel.tidy_hold::

$(datatel_hold_dirs)/ pattern=* ignore=*.txt ignore=*W2REPORT* age=${datatel_age_hold}

The processes Section

The process action is used to test for processes, signal processes, or restart processes

A regular expression is used to search output from the ps command to find the process to be acted on

A processes Example

processes:

modified_inetd_conf:: "inetd" signal=hup

no_snmp:: # Stop SNMP daemon

"snmpdx" signal=kill inform=true syslog=true

Feedback class

The shellcommands Section

Executes system commands or external scripts

Must specify full-path for security reasons Can specify owner, group, umask, etc. of

command

A shellcommands Example

shellcommands:

sunos_5_8|sunos_5_9::

# Fix tape device permissions.# Use a shell command because 'files' # section doesn't work very well# with symbolic links.

"/usr/bin/chmod 0770 /dev/rmt/*" "/usr/bin/chown root:sys /dev/rmt/*”

Some cfagent Runtime Options

-f Use the file name after this switch

-hHelp – display version banner and options summary

-n“All talk and no action.” Only print what has to be done without actually doing it.

-pParse the configuration file to check syntax and then stop.

-v Verbose mode: print detail information

cfagent Debugging Levels

-d Enable debugging output

-d1 Show only parsing output

-d2 Show only runtime action output

-d0 Both d1 and d2 levels output

Test, Test, Test

Modify actionsequence to test individual sections.

Use –p and –n options Run in verbose (-v) mode and save output Use –d options when desperate

Production

Simplest approach uses cron to call a script that runs cfagent instead of using cfexecd

Use a source-code control system for cfagent.conf file.

Be sure you have a good backup ….