LPI Linux Certification in a Nutshell, 2nd Edition

Objective 6: Troubleshooting Environment Configurations

In this section, we'll cover items not covered in previous sections.

Authorization Problems

Authorization problems are usually related to the /etc/passwd, /etc/shadow, and/or /etc/group files. Modern Linux systems offer other security systems that may be involved—notably Pluggable Authentication Modules (PAM) and SELInux, a series of patches made by the National Security Agency—but those are special cases and haven't shown up on the tests (yet!).

Generally speaking, problems related to these files are caused by hand-editing the files instead of using the system tools to modify them.

crontab Problems

The programs cron and at deal with scheduling jobs: cron continally reruns jobs according to schedules in the config files; at will execute a job just once at some future time.

Every user has a crontab file. They are located in /var/spool/cron on Red Hat- and Debian-based systems, On some systems, root's crontab file is considered personal to root and runs whatever root wants to schedule, while on other systems, root's crontab file is considered the system crontab file and is used to schedule system jobs.

There is also a global /etc/crontab on Red Hat systems that is used to schedule system jobs. This crontab file simply runs scripts (not other crontab files!) located in the directories /etc/cron.daily, /etc/cron.hourly, /etc/cron.weekly, and /etc/cron.monthly. The directory /etc/cron.d contains crontab files (not scripts!) ...