1. Linux Overview Why Linux ? Not-so-ancient history –Torvalds, Linus Torvalds, 002 the Helsinki University, as a student, low budget, work home –rapid and enthusiastic growth from toy to tool –ported to almost anything –from text mode servers to GUI desktops

2. Linux Overview Why Linux - continued A few good reasons –comes with its own sources: high degree of customization possible, most portable OS –stable server platform –wide range of support, from distributors and the community –leave the licensing adventure to the stronger-hearted

3. Linux Overview The Linux distribution (focus on Red Hat) Basic OS components of a UNIX system – the kernel – the heart of the OS – system programs – implement the various services required from an operating system – application programs – get useful things done

4. Linux Overview The bootloader –Choice of alternative OS –Sends boot parameters to the kernel –GRUB vs LILO User accounts, groups –Root account - no questions asked - careful The Linux distribution (focus on Red Hat)

5. Linux Overview The filesystem (common) –Root directory: files that are necessary for booting the system – /root : The home directory for user root. This is usually not accessible to other users on the system – /usr : commands, libraries, manual pages, and user utilities – /var : files that change: spool directories, logs – /bin, /sbin : system programs – /home : users accounts home directories – /etc : system configuration files – /proc : system info – /dev : special device files for all the devices – /mnt : predefined mount point for devices The Linux distribution (focus on Red Hat)

6. Linux Overview The package manager –What it does (as opposed to “make install”) –How it works, dependencies: install erase upgrade queries: finding installed packages, installed files –Rebuilding packages spec files The Linux distribution (focus on Red Hat)

7. Linux Overview [root@bummer download]# netstat -atun Proto Recv-Q Send-Q Local Address Foreign Address State tcp 0 0 0.0.0.0:6000 0.0.0.0:* LISTEN tcp 0 0 127.0.0.1:631 0.0.0.0:* LISTEN tcp 0 0 0.0.0.0:7741 0.0.0.0:* LISTEN tcp 0 0 192.168.1.64:52479 83.140.65.8:80 ESTABLISHED tcp 0 0 192.168.1.64:50956 83.140.65.8:80 ESTABLISHED tcp 0 0 192.168.1.64:48980 83.140.65.8:80 ESTABLISHED tcp 0 0 192.168.1.64:39254 192.168.1.199:993 ESTABLISHED tcp 0 0 192.168.1.64:53081 216.155.193.157:5050 ESTABLISHED tcp 0 0 192.168.1.64:49203 217.74.209.135:5223 ESTABLISHED tcp 0 0 192.168.1.64:40836 192.168.1.63:3389 ESTABLISHED Practical aspects - view open ports and check connections

8. Linux Overview firewalls filter open ports; scan from another machine Practical aspects - view open ports - continued

9. Linux Overview ntsysv lets you select system services to be started at boot time (for the current runlevel) chkconfig –list (all runlevels) Practical aspects – startup services

10. Linux Overview # less /etc/xinetd.d/ftp service ftp { socket_type = stream protocol = tcp wait = no user = root server = /usr/bin/ftpd disable = no only-from = 192.168.200.3 192.168.200.7 192.168.200.9 only-from += 192.168.200.10 192.168.200.12 172.16.0.0 no_access = 172.16.{1,2,3,10} access_times = 07:00-21:00 } Practical aspects – startup services (continued) – on demand services

11. Linux Overview Practical aspects – check your system find files modified within the last 24 hrs find / -mtime 1 spot largest files (numeric sort on 5 th col) ls –lR | sort +4n find which process uses most memory ps aux | sort +4n Check available space df -h

12. Linux Overview find packages containing string rpm –qa | grep string find files installed by a package rpm –ql find all files installed by Open Office packages rpm –ql $(rpm –qa| grep openoffice) | less find all files installed by each package for i in $(rpm -qa | sort); do echo $i; rpm -ql $i; done Practical aspects – the package manager

13. Linux Overview Practical aspects – patching the system System updates –deal with software bugs vulnerabilities –dependency checking up2date – use the source apt, yum