Intro to Linux (cont)

1. Intro to Linux (cont)

2. Week 2 Objectives • Intro to Linux cont ppt • Logs • Quotas • iptables • Linux boot ppt • Security goals ppt • Hands on • vi, software install / packages, CLI, config files, cron

3. log files • log files are often overlooked by newbies • log files are important • valuable system information • footprints left behind by system abusers and crackers • system log daemon • syslog default • /etc/syslog.conf • syslog-ng popular alternative • /etc/syslog-ng.conf

4. log files • syslog configuration file • log facilities sources of log entries • auth • authpriv • cron • log levels severity of log entries • emerge • alert • crit

5. log files • syslog-ng configuration file • significantly different syntax that syslog • more cumbersome • requires definition of: • sources of log entries • destinations of log entries

6. log files • if left unattended, log files grow without bound • it is possible to create a denial of service (DoS) on your own system by completely filling the /var/log partition • this is not a good thing!!!

7. log files • the real issue with log files is that they be read! • automated log file analyzers can be a big help in this area • crontab • define a time interval for review (nightly?) • must pick up next time where it left off last time! • daemon • faster notification that a crontab utility • but more CPU intensive

8. log files • log file analysis is greatly facilitated by maintaining a single aggregate log file • /var/log/messages • additional separate log files may be maintained as well for the convenience of the system administrator

9. quotas • quotas allow the system administrator to limit file system resources available to users • types • per user • per group • limits • hard limit • soft limit • grace periods

10. quotas • hard limit • can not be exceeded • offending file can not be saved! • soft limit • warning message • offending file can be saved!

11. quotas • steps to implement: • edit file /etc/fstab • /dev/hda3 /home /ext2 defaults,usrquota,grpquota 1 2 • create database files for quotas • touch /home/aquota.user /home/aquota.group • chmod 600 /home/aquota.usr /home/aquota.group • initialize database • quotacheck -avug • activate quotas • quotaon -ug /home

12. quotas • steps to implement: (cont'd) • system startup scripts (/etc/init.d/boot.local) • quotacheck -avug • quotaon -avug • edit /etc/crontab • 0 3 * * * root /sbin/quotacheck -avug

13. quotas • system administration commands: • quota -uv <user> u = user • quota -gv <group> g = group • quotaon -u <filesystem> a = all • quotaon -g <filesystem> v = verbose • quotaon -a • quotaoff -u <filesystem> • quotaoff -g <filesystem> • quotaoff -a

14. quotas • system administration commands: (cont'd) • quotacheck -u <filesystem> • quotacheck -g <filesystem> • quotacheck -a • edquota -u <user> define / modify • edquota -g <group> quotas! • repquota -u <filesystem> summary report • repquota -g <filesystem> quotas • repquota -a

15. iptables and firewalls • Linux has evolved significantly over the past five years regarding firewall software • kernel 2.0 ipfwadm • kernel 2.2 ipchains • kernel 2.4 iptables (netfilters) • each upgrade introduced additional capabilities and simpler syntax

16. iptables and firewalls • iptables focuses on five facets of packet movement into, across, and out from a gateway host • these five facets are represented by tables • PREROUTING • INPUT • FORWARD • OUTPUT • POSTROUTING

17. iptables and firewalls

18. iptables and firewalls • each table consists of rules pertaining to packets • source / source port • destination / destination port • interface • protocol: icmp, udp, tcp • each rule specifies and action • -j ACCEPT • -j DROP no answer to sender • -j REJECT answer to sender

19. iptables and firewalls • rules within each table are processed in order • first rule to match triggers action • creating iptable rules is a non-trivial activity!

20. Package Management

21. RPM

22. Apt