The /etc/passwd file in Linux is a file that contains a list of users, and information about those users. We can use this file to list all users that exist in our system. For example, using the “cat” command will output the whole file. Notice that every line starts with the username field.

oot@bt:~# cat /etc/passwd
root:x:0:0:root:/root:/bin/bash
daemon:x:1:1:daemon:/usr/sbin:/bin/sh
bin:x:2:2:bin:/bin:/bin/sh
sys:x:3:3:sys:/dev:/bin/sh
sync:x:4:65534:sync:/bin:/bin/sync
games:x:5:60:games:/usr/games:/bin/sh
man:x:6:12:man:/var/cache/man:/bin/sh
lp:x:7:7:lp:/var/spool/lpd:/bin/sh
mail:x:8:8:mail:/var/mail:/bin/sh
news:x:9:9:news:/var/spool/news:/bin/sh
uucp:x:10:10:uucp:/var/spool/uucp:/bin/sh
proxy:x:13:13:proxy:/bin:/bin/sh
www-data:x:33:33:www-data:/var/www:/bin/sh
backup:x:34:34:backup:/var/backups:/bin/sh
list:x:38:38:Mailing List Manager:/var/list:/bin/sh
irc:x:39:39:ircd:/var/run/ircd:/bin/sh
gnats:x:41:41:Gnats Bug-Reporting System (admin):/var/lib/gnats:/bin/sh
libuuid:x:100:101::/var/lib/libuuid:/bin/sh
syslog:x:101:103::/home/syslog:/bin/false
sshd:x:102:65534::/var/run/sshd:/usr/sbin/nologin
landscape:x:103:108::/var/lib/landscape:/bin/false
messagebus:x:104:112::/var/run/dbus:/bin/false
nobody:x:65534:65534:nobody:/nonexistent:/bin/sh
mysql:x:105:113::/var/lib/mysql:/bin/false
avahi:x:106:114::/var/run/avahi-daemon:/bin/false
snort:x:107:115:Snort IDS:/var/log/snort:/bin/false
statd:x:108:65534::/var/lib/nfs:/bin/false
usbmux:x:109:46::/home/usbmux:/bin/false
pulse:x:110:116::/var/run/pulse:/bin/false
rtkit:x:111:117::/proc:/bin/false
festival:x:112:29::/home/festival:/bin/false
postgres:x:1000:1000::/home/postgres:/bin/sh

Now, if we want to refine our search and filter out all that extra information and just print the usernames, we can use the “awk” command like this:

awk -F ':' '{print $1}' /etc/passwd

In this command the “-F” option tells awk the separating field, in this case the colon “:”, and the {print $1} option, is just to print out the first field, which is the username field.

root@bt:~# awk -F ':' '{print $1}' /etc/passwd
root
daemon
bin
sys
sync
games
man
lp
mail
news
uucp
proxy
www-data
backup
list
irc
gnats
libuuid
syslog
sshd
landscape
messagebus
nobody
mysql
avahi
snort
statd
usbmux
pulse
rtkit
festival
postgres

Making a copy or backup of your MBR is very simple. There’s a couple of ways you can go about it. First one, using “dd” command, and second, using “sfdisk.”

The Master Boot Record is 512 bytes

446 Bootstrap + 64 Partition Table + 2 Signature = 512

Using “dd” with identical partitions

copying  

dd if=/dev/sdb of=sdbmbr.bak bs=512 count=1

restoring

dd if=sdbmbr.bak of=/dev/sdb bs=512 count=1

Using “dd” with different partitions (when restoring to a different partition size will keep original size).

copying

dd if=/dev/sdb of=sdbmbr.bak bs=512 count=1

restoring

dd if=sdbmbr.bak of=/dev/sdb bs=446 count=1

Using “sfdisk” linux command

copying

sfdisk -d /dev/sdb > ~/sdbmbr.bak

restoring

sfdisk /dev/sdb < sdbmbr.bak

If you’ve migrated to Ubuntu 11.10, and you’re having a hard time getting used to “Unity,” there’s hope!.. Well, sort of. You can install Gnome Classic, which will make the interface a bit more familiar, but still is gnome3, and it is a huge transformation from previous versions of gnome, but at least is not Unity. Gnome Classic is not installed by default so you’ll have to install it. And this is ubuntu with gnome classic installed.

1- Open terminal window and type

sudo apt-get install gnome-session-fallback

2- now log off and select “Gnome Classic” at login screen

In this tutorial we will go over on how to create a desktop shortcut or application launcher in Ubuntu 11.10. In previous version it was pretty easy to create a desktop launcher; you pretty much right click the desktop and create your launcher, but not so easy in this version of Ubuntu, and that’s what we are going to cover.

1- Open a terminal in Unity (dash windows->type “terminal”)

2- Install gnome-panel package

sudo apt-get install --no-install-recommends gnome-panel

3- Open the “Create Launcher” app by typing

gnome-desktop-item-edit ~/Desktop/ --create-new

4- Give it a name and the command to launch the application. In this case we’re using thunderbird.

Going through different log files can be a pain, but here’s a simple script that parses today’s logs from different files into a single file, in this case we extract today’s logs from messages, auth.log, syslog. Finally, we send them through email. Don’t forget to make the file executable!… Logparser can be downloaded from here

#!/bin/bash
#author jorge
#purpose: extracting daily log entries from multiple log files
 
LOG1=/var/log/messages
LOG2=/var/log/auth.log
LOG3=/var/log/syslog
MYDATE=`date +%b\ %d`
OUTPUTLOG=`date +%F`.dailylog
EMAIL=btuser
 
for LOG in $LOG{1,2,3}
do
        #if file exist and is not empty then process
        if [ -e $LOG ] && [ -s $LOG ]; then
                echo $LOG BEGIN >> $OUTPUTLOG
                #only grabbing todays log out of file
                grep -E "$MYDATE" $LOG >> $OUTPUTLOG 2>/dev/null
                echo $LOG END >> $OUTPUTLOG
                echo >> $OUTPUTLOG
        fi
done
 
#email output
cat $OUTPUTLOG | mail -s "daily logs `date +%F`" $EMAIL 2>/dev/null
 
#END

In past versions of ubuntu, I’ve experienced slow connections specially with internet. And it’s been because of IPv6. Now in Ubuntu 10.04, I didn’t noticed any slow connection; however, I decided to go ahead and disable it anyways… just in case. And here are the steps.

Checking whether IPv6 is enabled or not.

jorge@nixboxen:~$ cat cat /proc/sys/net/ipv6/conf/all/disable_ipv6
cat: cat: No such file or directory
1

if output=0 then is enabled. So use your preferred editor and open /etc/sysctl.conf. Then add the following lines.

#disable ipv6
net.ipv6.conf.all.disable_ipv6 = 1
net.ipv6.conf.default.disable_ipv6 = 1
net.ipv6.conf.lo.disable_ipv6 = 1

I decided to make a guide about TCP/IP configuration in Linux, and you may ask: well, what Linux distribution in specific? I know!, there are hundreds of Linux distribution, but for this guide, I’m only going to cover the two most used Linux distribution: Ubuntu and Fedora. Ubuntu is a Debian derivative, so the Ubuntu portion of TCP/IP configuration applies to any distro based on Debian. And the same goes for Fedora, which is based on RedHat Linux.

First, you want to find out what interfaces you have, and what ip address, “if any,” was assigned to your computer. For this use the “ifconfig” command:

ifconfig  #will list all enabled interfaces

if you are looking for a specific interface:

ifconfig eth0 #will only display the configuration for eth0 interface

If you get no interfaces other than the loopback address, it is time to do some troubleshooting and find out whether your network card was detected by Linux or not.

sudo lspci | grep -i ethernet #displaying all your ethernet cards

if you’re troubleshooting a wireless card just change “ethernet” for “wireless.”
other useful command when troubleshooting network card and drivers is “lsmod” Read the rest of this entry »