System Administration Guide: Security Services

Granting Access to Your Account

If you need to give someone access to log in to your account (as you), you can do so through Kerberos, without revealing your password, by putting a .k5login file in your home directory. A .k5login file is a list of one or more Kerberos principals corresponding to each person for whom you want to grant access. Each principal must be on a separate line.

Suppose that the user david keeps a .k5login file in his home directory that looks like the following:


This file allows the users jennifer and joe to assume david's identity, provided that they already have Kerberos tickets in their respective realms. For example, jennifer can remotely log in to david's machine (boston), as him, without having to give his password.

Figure 26–1 Using the .k5login File to Grant Access to Your Account

The preceding context describes the graphic.

In the case where david's home directory is NFS-mounted, using Kerberos V5 protocols, from another (third) machine, jennifer must have a forwardable ticket in order to access his home directory. See Creating a Kerberos Ticket for an example of using a forwardable ticket.

If you will be logging in to other machines across a network, you'll want to include your own Kerberos principal in .k5login files on those machines.

Using a .k5login file is much safer than giving out your password for these reasons:

One common way to use the .k5login file is to put it in root's home directory, giving root access for that machine to the Kerberos principals listed. This configuration allows system administrators to become root locally, or to log in remotely as root, without having to give out the root password, and without requiring anyone to type the root password over the network.

Example 26–4 Using the .k5login File to Grant Access to Your Account

Suppose jennifer decides to log in to the machine as root. Because she has an entry for her principal name in the .k5login file in root's home directory on, she again does not have to type in her password.

% rlogin -l root -x
This rlogin session is using DES encryption for all data transmissions.
Last login: Thu Jun 20 16:20:50 from daffodil
SunOS Release 5.7 (GENERIC) #2: Tue Nov 14 18:09:31 EST 1998