These log entries were written by the PAM libraries when the
crond daemon ran tasks in the background.
crond runs jobs on a schedule, on behalf of the system and the users on the system.
Every user has their own
crontab configuration file, which can be edited with the
crontab -e command or shown using
crontab -l. The system administrator can also configure jobs via a plethora of
/etc/ files and directories;
/etc/cron.d/ provides an easy place for services to drop their own configurations, and
/etc/crontab drives the
weekly directories, as well as runs whatever the administrator may choose to run.
crond will change users to the correct user (either specified in the
/etc/crontab file and the
/etc/cron.d/ directory, or from the user-supplied
crontab files) before running the jobs; it uses the PAM system to change users.
PAM provides a single place to configure different ways to authenticate and authorize users and provide session setup, as well as provide a way to change passwords (or other authentication tokens). Every service that uses PAM has a configuration file in
/etc/pam.d/ that describes which PAM modules to use when 'logging in' a user.
/etc/pam.d/cron file looks like this:
# The PAM configuration file for the cron daemon
# Read environment variables from pam_env's default files, /etc/environment
# and /etc/security/pam_env.conf.
session required pam_env.so
# In addition, read system locale information
session required pam_env.so envfile=/etc/default/locale
# Sets up user limits, please define limits for cron tasks
# through /etc/security/limits.conf
session required pam_limits.so
This ensures limits that are configured for users are applied to users' tasks when they run them via
cron. If you wanted to change those limits per-service, you could configure
pam_limits.so in this file with your own
conf=/etc/security/cron-limits.conf and apply different limits than ssh logins (
/etc/pam.d/sshd) or console logins (