artemn@artemn-laptop:~$ cat /etc/passwd | awk '{print length, $0}' | sort -n | awk '{$1=""; print $0 }'

bin:x:2:2:bin:/bin:/bin/sh
sys:x:3:3:sys:/dev:/bin/sh
root:x:0:0:root:/root:/bin/bash
proxy:x:13:13:proxy:/bin:/bin/sh
mail:x:8:8:mail:/var/mail:/bin/sh
lp:x:7:7:lp:/var/spool/lpd:/bin/sh
sync:x:4:65534:sync:/bin:/bin/sync
ntp:x:110:120::/home/ntp:/bin/false
daemon:x:1:1:daemon:/usr/sbin:/bin/sh
ftp:x:111:65534::/home/ftp:/bin/false
games:x:5:60:games:/usr/games:/bin/sh
klog:x:102:103::/home/klog:/bin/false
man:x:6:12:man:/var/cache/man:/bin/sh
irc:x:39:39:ircd:/var/run/ircd:/bin/sh
dhcp:x:100:101::/nonexistent:/bin/false
news:x:9:9:news:/var/spool/news:/bin/sh
saned:x:120:131::/home/saned:/bin/false
syslog:x:101:102::/home/syslog:/bin/false
uucp:x:10:10:uucp:/var/spool/uucp:/bin/sh
backup:x:34:34:backup:/var/backups:/bin/sh
www-data:x:33:33:www-data:/var/www:/bin/sh
libuuid:x:112:121::/var/lib/libuuid:/bin/sh
messagebus:x:103:109::/var/run/dbus:/bin/false
nobody:x:65534:65534:nobody:/nonexistent:/bin/sh
sshd:x:109:65534::/var/run/sshd:/usr/sbin/nologin
Debian-exim:x:117:128::/var/spool/exim4:/bin/false
artemn:x:1000:1000:artemn,,,:/home/artemn:/bin/bash
list:x:38:38:Mailing List Manager:/var/list:/bin/sh
mysql:x:119:130:MySQL Server,,,:/var/lib/mysql:/bin/false
gdm:x:108:118:Gnome Display Manager:/var/lib/gdm:/bin/false
hplip:x:104:7:HPLIP system user,,,:/var/run/hplip:/bin/false
pulse:x:113:123:PulseAudio daemon,,,:/var/run/pulse:/bin/false
polkituser:x:114:127:PolicyKit,,,:/var/run/PolicyKit:/bin/false
avahi:x:106:114:Avahi mDNS daemon,,,:/var/run/avahi-daemon:/bin/false
asterisk:x:118:129:Asterisk PBX daemon,,,:/var/lib/asterisk:/bin/false
gnats:x:41:41:Gnats Bug-Reporting System (admin):/var/lib/gnats:/bin/sh
haldaemon:x:107:116:Hardware abstraction layer,,,:/home/haldaemon:/bin/false
landscape:x:115:65534:Landscape Client Daemon,,,:/var/lib/landscape:/bin/false
avahi-autoipd:x:105:113:Avahi autoip daemon,,,:/var/lib/avahi-autoipd:/bin/false
chipcard:x:116:119:Chipcard-Tools Daemon Account,,,:/var/run/chipcard:/bin/false

For reverse sort, use the following command:

cat /etc/passwd | awk '{print length, $0}' | sort -rn | awk '{$1=""; print $0 }'

Source: www.opennet.ru

ethtool

This is rather powerful utility can display and change settings of ethernet network interface card. You can easily disable/enable autonegotiation option for your NIC, also it’s possible to manually set up duplex mode, configure wake-on-lan options, set speed settings. Just look through full manual page for ethtool. Here are several ethtool usage examples:

ethtool eth0 – shows current NIC settings

Settings for eth0:
        Supported ports: [ TP MII ]
        Supported link modes:   10baseT/Half 10baseT/Full
                                100baseT/Half 100baseT/Full
        Supports auto-negotiation: Yes
        Advertised link modes:  10baseT/Half 10baseT/Full
                                100baseT/Half 100baseT/Full
        Advertised auto-negotiation: No
        Speed: 10Mb/s
        Duplex: Half
        Port: MII
        PHYAD: 32
        Transceiver: internal
        Auto-negotiation: off
        Supports Wake-on: pumbg
        Wake-on: d
        Current message level: 0x00000007 (7)
        Link detected: yes

ethtool -s eth0 duplex half autoneg off – disables auto-negotiation, enables Half Duplex.
ethtool -s eth1 duplex full speed 1000 autoneg off – disables auto-negotiation, enables Falf Duplex and sets up Speed to 1000 Mb/s.

mii-tool

According to manual it allows to manipulate and see media-independent interface status. Let’s see examples:

bash-3.1# mii-tool eth0
eth0: negotiated 100baseTx-FD, link ok – shows 100 Mbps speed, Full Duplex, Auto-negotiation is on.
bash-3.1# mii-tool eth0 -F 10baseT-HD – enables 10 Mb/s Half Duplex connection.

A: In GNU Screen press Ctrl + a + [ to enter Copy Mode, then scroll up/down using keys j or k. Below are some other navigation keys:

h -    Move the cursor left by one character
j -    Move the cursor down by one line
k -    Move the cursor up by one line
l -    Move the cursor right by one character
0 -    Move to the beginning of the current line
$ -    Move to the end of the current line.
G -    Moves to the specified line
       (defaults to the end of the buffer).
C-u -  Scrolls a half page up.
C-b -  Scrolls a full page up.
C-d -  Scrolls a half page down.
C-f -  Scrolls the full page down.

By the way, in order to define scrollback buffer size start screen with the following key (5000 lines in this example):

screen -h 5000

Quick info about GNU Screen utility: it is Unix tool that allows to run multiple applications in several “virtual” windows. It is very useful when you need, let’s say, to see hardware resources consumption caused by started application in different console etc. GNU screen is also good option to run applications remotely via ssh: just run application in screen and log off until it’s finished, then just “pick up” screen session and see how the application’s output.

Update: You can use activate copy mode of GNU Screen also by Ctrl + Esc that might be more useful than Ctrl + a + [ shortcut (thanks to Yu-Jie Lin for this tip).

Answer: Sure, below are the links to extremely informative Internet resources providing detailed guides on why and how to deploy MySQL cluster.

By the way a cluster in IT field is a group of linked computers, working together so they form a single computing system. The components of a cluster are usually connected to each other via fast local area networks. Clusters are usually deployed to improve performance and/or availability over that provided by a single computer, while typically being much more cost-effective than single computers of comparable speed or availability.

1. http://dev.mysql.com/doc/refman/5.0/en/mysql-cluster.html

MySQL Cluster is a high-availability, high-redundancy version of MySQL adapted for the distributed computing environment. It uses the NDBCLUSTER storage engine to enable running several MySQL servers in a cluster. This storage engine is available in MySQL 5.0 binary releases and in RPMs compatible with most modern Linux distributions.

2. Mysql Cluster: The definitive HOWTO

3. How To Set Up A Load-Balanced MySQL Cluster

This tutorial shows how to configure a MySQL 5 cluster with three nodes: two storage nodes and one management node. This cluster is load-balanced by a high-availability load balancer that in fact has two nodes that use the Ultra Monkey package which provides heartbeat (for checking if the other node is still alive) and ldirectord (to split up the requests to the nodes of the MySQL cluster).

4. MySQL Cluster Server Setup

MySQL Cluser Server is a fault-tolerant, redundant, scalable database architecture built on the open-source MySQL application, and capable of delivering 99.999% reliability. In this paper we describe the process we used to setup, configure, and test a three-node mySQL cluster server in a test environment.

Question

Answer: There is an iptables module named OSF (passive OS Fingerprinting) that was written by Evgeniy Polyakov. This module allows passively detect OS packet was sent from and perform various netfilter actions based on this match. Packets with SYN bit set are analyzed.

In order to install OSF module, do the following:

1. Download latest release from here, for example as follows:
wget http://tservice.net.ru/~s0mbre/archive/osf/osf-2008_06_14.tar.gz

2. Edit Makefile from unpacked archive in order to set proper path to iptables headers (iptables.h and libiptc/ dir).

3. If your kernel sources can not be accessed via /lib/modules/$(shell uname -r)/build, you have to replace KDIR variable with the correct path to kernel sources.
4. Run make that should build ipt_osf.ko kernel module.
5. Run make lib that will build libipt_osf.so shared library (copy it to where all other iptables shared libs are placed in your distro e.g. /lib/iptables or /lib64/iptables in Fedora).

6. Run make bin that will build userspace applications which allows to load fingerprints and obtain information about matched packets (load, osfd, ucon_osf).

7. Download signatures list:
wget http://www.openbsd.org/cgi-bin/cvsweb/src/etc/pf.os

8. Install kernel module:
insmod ./ipt_osf.ko

9. Load signatures:
./load ./pf.os /proc/sys/net/ipv4/osf

10. Set up iptables rules allowing/disallowing packets generated by certain OS:
iptables -I INPUT -j ACCEPT -p tcp -m osf --genre Linux --log 0 --ttl 2

This example allows traffic from Linux systems and logs packets from other ones:
ipt_osf: Windows [2000:SP3:Windows XP Pro SP1, 2000 SP3]: 11.22.33.55:4024 -> 11.22.33.44:139

BTW, OSF has following options:

• –log
  If present, OSF will log determined genres even if they don’t match desired one.
  0 – log all matched and unknown entries.
  1 – only first one.
  2 – log all matched entries.
• –ttl
  0 – true ip and fingerprint TTL comparison. Works for LAN.
  1 – check if ip TTL is less than fingerprint one. Works for global addresses.
  2 – do not compare TTL at all. Allows to detect NMAP, but can produce false results.
• –connector
  If present, OSF will log all events also through netlink connector(1.0 id).
  More about connector can be found in Documentation/connector in kernel source tree.

Question

Answer: As you might know, kernel panic is an action taken by an operating system upon detecting an internal fatal error from which it cannot safely recover; the term is largely specific to Unix and Unix-like systems (it’s a wiki’s description).

By default Linux wouldn’t not reboot after panic occurs, but the following option of sysctl will cause a kernel to reboot after N seconds you specify. In our example server will be rebooted in 15 seconds if kernel panic stopped its operation:

1. Open sysctl’s configuration file:
sudo nano /etc/sysctl.conf

2. Add there the following line:
kernel.panic = 15

or

1. Execute the following command:
/sbin/sysctl -w kernel.panic=15

Hope it helps!

Answer: Actually you are totally right that you wish to disable this feature. One of the “must do’s” on setting a secure apache web server is to disable directory browsing. Usually apache comes with this feature enabled but its always a good idea to get it disabled unless you really need it.

First of all find where is the main apache’s config file httpd.conf is located. If you use Debian, it should be here: /etc/apache/httpd.conf. Using some file editor like Vim or Nano open this file and find the line that looks as follows:

Options Includes Indexes FollowSymLinks MultiViews

then remove word Indexes and save the file. The line should look like this one:

Options Includes FollowSymLinks MultiViews

After it is done, restart apache (e.g. /etc/init.d/apache restart in Debian). That’s it!

Answer: You can use application named as “netselect-apt” to get new sources.list file with fastest APT mirror. Install this application by command "sudo aptitude install netselect-apt" and run it in accordance with Debian distribution you use (Debian Etch in our example):

sudo netselect-apt -n etch -o /etc/apt/sources.list
sudo apt-get update

P.S. By the way, in Ubuntu you can do the same in a few clicks.

Answer: There are two commands in Linux CLI coming by default which would help to unload drivers: rmmod and modprobe. First of all it is necessary to find what kernel module controls certain NIC and then unload that module. For example, you have VIA VT6102 (RHINE-II) network card that is recognized by Linux as eth0 and want to disable its driver temporarily. Just execute the following:

“sudo rmmod via-rhine” or “sudo modprobe -r eth0” (or “sudo modprobe -r via-rhine“). You can use command dmesg to determine the name of kernel module you wish to unload.

Answer: You are welcome to use iptables patch-o-matic extension (pom or p-o-m) that allows you to match a packet based on its arrival or departure (for locally generated packets) timestamp. The syntax is the following:

iptables RULE -m time --timestart TIME --timestop TIME --days DAYS -j ACTION

Where:

--timestart TIME: Time start value (format is 00:00-23:59)
--timestop TIME: Time stop value (the same format)
--days DAYS: a list of days to apply, from (format: Mon, Tue, Wed, Thu, Fri, Sat, Sun).

To add the rule stated in the question use the following command:

iptables -A INPUT -p tcp -d 192.168.0.1 --dport 22 -m time --timestart 19:00 --timestop 8:00 -days Mon,Tue,Wed,Thu,Fri -j DROP

Hope it helps!