Setting up LDAP 

Now

that we’ve seen what a directory is, and how it stores data, we can get on

with setting up an  LDAP server under Linux and use it to centralize

network resource information. Here, we’ll configure an LDAP server to

authenticate and manage network resource information for a Linux-only

network.

Setting up and Configuring

OpenLDAP

The

accompanying Red Hat 6.2 (Zoot) CD comes with OpenLDAP project’s LDAP

server. OpenLDAP is based on the code of the University of Michigan’s

original LDAP server. The OpenLDAP distribution includes both slapd (the

directory server) and slurpd (the replication server), as well as several

tools and libraries. Also, several accompanying packages are bundled to

allow you to easily reconfigure the system to use LDAP for authentication.

To install the LDAP server,

mount the zoot CD-ROM, and run the command:

# rpm -ivh /mnt/cdrom/RedHat/RPMS/openldap*.rpm

This will install both the

server and the development packages.

All the remaining LDAP

support packages are pre-installed on your system (as part of pam and

nss_ldap)

The LDAP configuration files

are stored in the directory /etc/openldap.

Become root, and edit the

file /etc/openldap/slapd.conf.

Here, modify the suffix entry

for your domain name (for example, the domain pcquest.com becomes)

suffix dc=pcquest,dc=com

Set up a rootdn (the root, or

manager’s distinguished name)

rootdncn=Manager,dc=pcquest,

dc=com

The "Manager" entry

should specifically not be any user on the network.

Set up a password for the

Manager. As the warning suggests, cleartext passwords are a bad idea. Find

out how to add an encrypted entry and do it. For now, we’ll stick with a

cleartext entry.

rootpw secret

That should be sufficient to

get your LDAP server up and running. Note that we haven’t configured

slurpd, which is the replication server. It isn’t necessary to be running

slurpd, but if you’re planning to use the setup in a production

environment, it’s definitely a good idea to have it up.

Let’s continue with

configuring the directory server–slapd.

Start slapd with the command

# /etc/rc.d/init.d/ldap

start

Now, we can

get down to the task of entering network resource information into the

directory service.

To understand what logrotate can do....

To understand what logrotate

can do, first ask yourself what you want to do with your log files. The

table "Planning for a log processing and archiving policy" might

help you to start. The first row lists the processing and reporting to be

done, while the first column lists the files on which the processing is to

be done. Put down the different log files in column 1, tick out the log

processing of your choice, and you can come up with a policy for using

logrotate.

Let me briefly explain what

each column implies. A "yes" on column 2 indicates that you want

to retain the log file as a record, so it’s best kept compressed.

Similarly, a "yes" in column 3 indicates that you merely want to

scan the file, look for the unusual, and then discard it. You might want to

mail this file to yourself or to the relevant administrator. Column 4 says

that you want to discard the file straightaway. In the sysadmin world, this

obviously doesn’t qualify for best practice. Columns 5 and 6

mention the actions you want to perform before and after you do the log

processing. Column 7 is for an e-mail address to which errors during log

processing are to be reported, and column 8 indicates how often you want the

processing to be done. Note that you might want a time threshold with a

granularity of a day or choose to have a file size threshold to rotate the

logs. This table is not exhaustive or mandatory in nature–it’s is merely

an example of how you would go about the policy-making exercise. So, don’t

implement this, as is, as a policy. Evolve one to suit your needs.

If you’re ready with a

table such as the one above, you have a policy. You can now use logrotate to

implement this policy.

The policy is specified using

keywords, as well as with a script-like language comprising keywords

specific to logrotate. The script is intuitive and easy to understand. By

default, most logs are rotated four times, uncompressed, before they’re

removed from the system. This should explain the presence of files with the

extensions .1, .2, .3 and .4 in the /var/log directory. Take the file /var/log/messages

as an example. After a certain time period or after a certain file size is

reached (as specified in /etc/logrotate. conf), this file is renamed to

messages.1 and an empty file called messages is created to take in the new

log input. This is repeated until they’re rotated four times.

Let’s look at a portion of

the configuration from /etc/logrotate.conf from a standard install. The

first line mentions the name of the file for which the policy is laid out.

Notice the intuitive keywords–"monthly" indicates that the

rotation cycle is monthly, "create" specifies the permissions and

ownerships to be used when the old file is moved to another name and an

empty file is created. "Rotate 1" indicates that one rotated

logfile will be retained:

/var/log/wtmp

{ monthly

create 0664

root utmp

rotate 1

}

Here’s a portion of the

file /etc/logrotate.d/apache–the policy for processing apache log files.

The keyword missingok implies that if the log file isn’t found, continue

processing the rest. Notice the command in between the keywords postrotate

and endscript. This command is executed after log processing is done.

Surprisingly, you don’t find any other instructions such as the frequency

of rotation or the number of rotations, as in the previous case. When there’s

no explicit mention made, the definitions in the global configuration file

will apply.

/var/log/httpd/access_log

{

missingok

postrotate

/usr/bin/killall -HUP httpd 2> /dev/null || true

endscript

}

logrotate is typically run

once a day by the cron. If you are logged in as superuser, you would see an

entry similar to the one below in the crontab file:

0 0 * * * /usr/sbin/logrotate

The utility runs every

midnight. You can run it more often if you need to.

A good start towards

minimizing disk storage space would be to uncomment the compress option in

/etc/logrotate. conf, so that all the rotated log files are kept compressed.

Avinash

Shenoy is a systems and network administrator at the NCBS, Bangalore,

and Gopi Garge is a technology

consultant with Exocore Consulting <www.exocore.com>