# MIT Kerberos Documentation

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# Installing and configuring UNIX client machines

The Kerberized client programs include kinit, klist, kdestroy, and kpasswd. All of these programs are in the directory `/usr/bin`.

You can often integrate Kerberos with the login system on client machines, typically through the use of PAM. The details vary by operating system, and should be covered in your operating system’s documentation. If you do this, you will need to make sure your users know to use their Kerberos passwords when they log in.

You will also need to educate your users to use the ticket management programs kinit, klist, and kdestroy. If you do not have Kerberos password changing integrated into the native password program (again, typically through PAM), you will need to educate users to use kpasswd in place of its non-Kerberos counterparts passwd.

## Client machine configuration files

Each machine running Kerberos should have a krb5.conf file. At a minimum, it should define a default_realm setting in [libdefaults]. If you are not using DNS SRV records (Hostnames for KDCs) or URI records (KDC Discovery), it must also contain a [realms] section containing information for your realm’s KDCs.

Consider setting rdns to false in order to reduce your dependence on precisely correct DNS information for service hostnames. Turning this flag off means that service hostnames will be canonicalized through forward name resolution (which adds your domain name to unqualified hostnames, and resolves CNAME records in DNS), but not through reverse address lookup. The default value of this flag is true for historical reasons only.

If you anticipate users frequently logging into remote hosts (e.g., using ssh) using forwardable credentials, consider setting forwardable to true so that users obtain forwardable tickets by default. Otherwise users will need to use `kinit -f` to get forwardable tickets.

Consider adjusting the ticket_lifetime setting to match the likely length of sessions for your users. For instance, if most of your users will be logging in for an eight-hour workday, you could set the default to ten hours so that tickets obtained in the morning expire shortly after the end of the workday. Users can still manually request longer tickets when necessary, up to the maximum allowed by each user’s principal record on the KDC.

If a client host may access services in different realms, it may be useful to define a [domain_realm] mapping so that clients know which hosts belong to which realms. However, if your clients and KDC are running release 1.7 or later, it is also reasonable to leave this section out on client machines and just define it in the KDC’s krb5.conf.