Ubuntu/Quick Reference

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Enable Remote Desktop via VNC (12.04+ - these are just default, you may want to configure more)

Dash Home > [type] Desktop > [Select] either Desktop Sharing or Remote Desktop
[check] Allow view and control > [check] require user to enter password > [type] password

Upgrade from 10.04LTS to 12.04LTS via terminal

$ sudo apt-get update
$ sudo apt-get install update-manager-core
$ sudo vi /etc/update-manager/release-upgrades
verify there is the following line in the file
prompt=lts
$ sudo apt-get update && sudo apt-get -y upgrade && sudo apt-get -y autoremove
$ sudo do-release-upgrade -d

rename directory with contents

~$ sudo mv -f /path/oldfolderanem /path/newfoldername

ubuntu 14.04 apt-get error

W: GPG error: http://archive.ubuntu.com trusty Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 40976EAF437D05B5 NO_PUBKEY 3B4FE6ACC0B21F32

Keys are:

40976EAF437D05B5
3B4FE6ACC0B21F32

fix by importing keys from Canonical's key library:

~$sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 3B4FE6ACC0B21F32
~$sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 40976EAF437D05B5

ubuntu 14.04 locale error

error
perl: warning: Setting locale failed.
perl: warning: Please check that your locale settings:
	LANGUAGE = (unset),
	LC_ALL = (unset),
	LANG = "en_US.UTF-8"
    are supported and installed on your system.
perl: warning: Falling back to the standard locale ("C").
solution

1. check what locales you have available on the machine

~$ locale -a
locale: Cannot set LC_CTYPE to default locale: No such file or directory
locale: Cannot set LC_MESSAGES to default locale: No such file or directory
locale: Cannot set LC_COLLATE to default locale: No such file or directory
C
C.UTF-8
POSIX

2. if you're missing the locale for your area like i was, you can sometimes discover the name

~$ locale
locale: Cannot set LC_CTYPE to default locale: No such file or directory
locale: Cannot set LC_MESSAGES to default locale: No such file or directory
locale: Cannot set LC_ALL to default locale: No such file or directory
LANG=en_US.UTF-8
LANGUAGE=
LC_CTYPE="en_US.UTF-8"
LC_NUMERIC="en_US.UTF-8"
LC_TIME="en_US.UTF-8"
LC_COLLATE="en_US.UTF-8"
LC_MONETARY="en_US.UTF-8"
LC_MESSAGES="en_US.UTF-8"
LC_PAPER="en_US.UTF-8"
LC_NAME="en_US.UTF-8"
LC_ADDRESS="en_US.UTF-8"
LC_TELEPHONE="en_US.UTF-8"
LC_MEASUREMENT="en_US.UTF-8"
LC_IDENTIFICATION="en_US.UTF-8"
LC_ALL=

3. once you know which locale you need, you can build it

~$ sudo locale-gen en_US.UTF-8
Generating locales...
  en_US.UTF-8... done
Generation complete.

4. make sure it's up to date (which is should be)

~$ sudo dpkg-reconfigure locales
Generating locales...
  en_US.UTF-8... up-to-date
Generation complete.

5. check to see if the new locale is listed and verify you no longer get the error

~$ locale -a
C 
C.UTF-8
en_US.utf8
POSIX

You'll see here that unlike in step 1, you get the required responses without an error message.

search for directories recursively and add execute permission

~$ find /var/www/mysite.com/ -type d -exec chmod+x {} \;


port scan from behind a firewall to determine which ports are open

first, there are a couple of things you'll need:

  1. linux box inside the firewall with nmap installed
  2. linux box outside the firewall with tcpdump installed


essentially, we are going to use nmap to port scan the box outside the firewall from inside, then look at the tcpdump logs and determine which packets got there and what ports they were destined for.

setup tcpdump

setup tcpdump to capture the traffic on the outside box

~$ tcpdump -i <interface> -n <source>
i.e. ~$ sudo tcpdump -i venet0:0 -n "src host 8.8.8.8 and not (dst port 80 or dst port 443)" -w port_scan.cap

In my example above, i went 1 extra step and said not to capture any packets going to port 80 or 443. I did this because I saw my firewall had a nifty little feature where it redirected traffic for restricted ports to 80 and 443, so because I already knew these were open, I could determine that any traffic hitting these ports was from redirected blocked ports.

scan with nmap

use nmap from the inside box

~$ nmap -p 1-65535 8.8.8.8

Simple nmap scan of all ports from 1 to 65535 (which are all available ports). The wildcard scan "*" didnt work as well as this did and i got a few more results.

parse the pcap

Once your nmap is done, now we can go back to our box on the outside, stop the tcpdump and start parsing it.

convert to txt
first lets convert the pcap to txt
~$ tcpdump -n -r portscan.cap > port_scan.txt
look at the txt
really quickly, this is an example of the txt output from our pcap
03:43:59.008245 IP 4.2.2.2.53008 > 8.8.8.8.10443: Flags [S], seq 1225698019, win 14600, options [mss 1380,sackOK,TS val 153049091 ecr 0,nop,wscale 7], length 0
parse the txt
now lets extract just the port numbers we care about
~$awk '{print $5;}' port_scan.txt  | sed 's/8.8.8.8.//g' | sed 's/://g'

To break down the example above:

  1. awk uses whitespaces as delimiters by default, so its easy to see the 2nd IP listed with the port is the 5th object.
  2. the first sed then looks for the outside box's IP, and replaces it with nothing (deleting it)
  3. the second sed cleans it up by replacing the colon after the port with nothing (deleting it)


results

So in the end, you end up with a nice list of open ports, like such:

~$ awk '{print $5;}' port_scan.txt  | sed 's/8.8.8.8.//g' | sed 's/://g'
22
8080
22
22
8173
8173
43
43
5050
5050
15210
15210
1003
1003
8082
10443
10443

Spoof MAC address and connect to network without rebooting

Took me awhile to figure out what series of events would allow me to spoof a MAC address, obtain a new DHCP lease and IP address, and connect to the network without rebooting. Turns out it was super simple.
If ifdown doesn't work and says something about interface eth0 not configured, try rebooting. Even a fresh install of 14.04 encountered this issue.

turn down interface
~$ sudo ifdown eth0
spoof MAC
~$ sudo ifconfig eth0 hw ether xx:xx:xx:xx:xx:xx
turn up interface
~$ sudo ifup eth0

From here if you run ifconfig you should see your interface with the new MAC address and DHCP lease with IP address.

find network settings of local interface

~$ nm-tool

NetworkManager Tool

State: connected (global)

- Device: eth1  [Wired connection 2] -------------------------------------------
  Type:              Wired
  Driver:            r8169
  State:             connected
  Default:           yes
  HW Address:        00:11:22:33:44:55

  Capabilities:
    Carrier Detect:  yes
    Speed:           1000 Mb/s

  Wired Properties
    Carrier:         on

  IPv4 Settings:
    Address:         10.0.0.241
    Prefix:          24 (255.255.255.0)
    Gateway:         10.0.0.3

    DNS:             10.0.0.3
    DNS:             127.0.0.1

Ubuntu Desktop 14.04 - unable to resolve hostnames except through dig

Weird issue, after setting up a local Zentyal server with DNS enabled, I could look up the DNS records I created by using dig, but any other commands, like ping, would not resolve the hostname. Neither would any browsers.
I found out that my /etc/nsswitch.conf file had this setup for hosts:

hosts: files mdns4_minimal [NOTFOUND=return] dns

So I changed it to this:

hosts: dns files wins

Rebooted and now everything works.

Expand root disk on VM

In this scenario, I needed to expand the disk on a non-LVM ubuntu installation. Nothing particularly special about this setup thankfully, just has the default partition configuration:

~$ sudo fdisk -l
....
Device     Boot    Start      End  Sectors Size Id Type
/dev/sda1  *        2048 75497471 75495424  36G 83 Linux
/dev/sda2       75499518 83884031  8384514   4G  5 Extended
/dev/sda5       75499520 83884031  8384512   4G 82 Linux swap / Solaris

Expand disk in hypervisor

To start things off, we need to expand the disk in the hypervisor. In my case I was using SCVMM atop Hyper-V, so I just powered off the virtual machine > VM properties > hardware configuration > Disk > Expand virtual disk.
Your hypervisor may be different.

Confirm the disk has been expanded (but filesystem has not been). Notice in this example /dev/sda is 100GB.

~$ sudo lsblk
NAME   MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
fd0      2:0    1    4K  0 disk
sda      8:0    0  100G  0 disk
├─sda1   8:1    0   38G  0 part /
├─sda2   8:2    0    1K  0 part
└─sda5   8:5    0    2G  0 part [SWAP]
sr0     11:0    1 1024M  0 rom

Disable swap and remove partitions

With the root partition starting from the beginning of the disk, in order to expand it the swap partition has to be deleted and recreated. Thankfully since the swap should not be mounted, this is pretty easy.

~$ sudo swapoff -a
~$ sudo lsblk
NAME   MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
fd0      2:0    1    4K  0 disk
sda      8:0    0  100G  0 disk
├─sda1   8:1    0   38G  0 part /
├─sda2   8:2    0    1K  0 part
└─sda5   8:5    0    2G  0 part
sr0     11:0    1 1024M  0 rom

Before we can delete the swap partition(s), we need to discover the disk name and the partition number(s)

~$ sudo parted -l
Model: Msft Virtual Disk (scsi)
Disk /dev/sda: 107GB
Sector size (logical/physical): 512B/4096B
Partition Table: msdos
Disk Flags:

Number  Start   End     Size    Type      File system     Flags
 1      1049kB  40.8GB  40.8GB  primary   ext4            boot
 2      40.8GB  42.9GB  2145MB  extended
 5      40.8GB  42.9GB  2145MB  logical   linux-swap(v1)

Now we can delete the swap(s).

~$ sudo parted /dev/sda rm 2
Information: You may need to update /etc/fstab.

Since the logical is within the extended partition, when you remove it, it removes both.
If you needed to check for mounts on the partition, you could use mount

~$ sudo mount
sysfs on /sys type sysfs (rw,nosuid,nodev,noexec,relatime)
proc on /proc type proc (rw,nosuid,nodev,noexec,relatime)
udev on /dev type devtmpfs (rw,nosuid,relatime,size=1000664k,nr_inodes=250166,mode=755)
...

Extend root partition

WARNING: the following section is HACKY to say the least. Unfortunately i dont know a better way of doing it yet.

First, we need to create a partition at the end of the drive which will eventually become our new swap space. I'm going to create it using parted as it will easily let me correctly position the partition.
NOTE: parted will only create a Win95 Extended partition, not just an Extended. I'm not sure if it matters or not but I will later recreate this partition using fdisk.

~$ sudo parted -s -a optimal /dev/sda unit GiB mkpart Extended 98GiB 100%
~$ fdisk -l
...
Device     Boot     Start       End  Sectors Size Id Type
/dev/sda1  *         2048  79691775 79689728  38G 83 Linux
/dev/sda2       205520896 209715199  4194304   2G  f W95 Ext'd (LBA)

With the partition in place we can now extend the root, which we can do with growpart.

~$ sudo apt install -y cloud-guest-utils
~$ sudo growpart /dev/sda 1
CHANGED: partition=1 start=2048 old: size=79689728 end=79691776 new: size=205518848,end=205520896

And we next need to expand the filesystem on the root partition.

~$ sudo resize2fs /dev/sda1

Create new swap partitions

With the root partition extedned, we need to recreate our swap partition(s). We are going to setup a new Extended partition at the new end of the disk. I've chosen 2GB as my RAM is set to 2GB. We are using fdisk as I do not know of another way to create an Extended partition that is not a "Win95 Extended" partition.

 ~$ sudo parted /dev/sda rm 2
~$ ~$ sudo fdisk /dev/sda

Welcome to fdisk (util-linux 2.27.1).
Changes will remain in memory only, until you decide to write them.
Be careful before using the write command.


Command (m for help): n
Partition type
   p   primary (1 primary, 0 extended, 3 free)
   e   extended (container for logical partitions)
Select (default p): e
Partition number (2-4, default 2): 2
First sector (205520896-209715199, default 205520896):
Last sector, +sectors or +size{K,M,G,T,P} (205520896-209715199, default 209715199):

Created a new partition 2 of type 'Extended' and of size 2 GiB.

Command (m for help): w
The partition table has been altered.
Calling ioctl() to re-read partition table.
Re-reading the partition table failed.: Device or resource busy

The kernel still uses the old table. The new table will be used at the next reboot or after you run partprobe(8) or kpartx(8).

Check your work:

sudo fdisk -l
...
Device     Boot     Start       End   Sectors Size Id Type
/dev/sda1  *         2048 205520895 205518848  98G 83 Linux
/dev/sda2       205520896 209715199   4194304   2G  5 Extended

Finally we want to create a logical drive on top our extended partition. Using the sector start we get from fdisk -l we need to add (+1) sector to the start positioning.

~$ sudo parted -s -a optimal /dev/sda unit s mkpart logical linux-swap 205520897 100%

This will result in the logical swap partition we want.

~$ sudo fdisk -l
Device     Boot     Start       End   Sectors Size Id Type
/dev/sda1  *         2048 205520895 205518848  98G 83 Linux
/dev/sda2       205520896 209715199   4194304   2G  5 Extended
/dev/sda5       205520897 209715199   4194303   2G 82 Linux swap / Solaris

Create filesystem and enable swap

Now let's create the filesystem on our new swap.

~$ sudo mkswap /dev/sda5
mkswap: warning: /dev/sda5 is misaligned
Setting up swapspace version 1, size = 2 GiB (2147475456 bytes)
no label, UUID=c9462e3f-f306-484e-b8b4-cf4a680fab87
~$ sudo swapon /dev/sda5

Now using our new UUID we can update fstab so that the new swap is used on boot.

~$ sudo vim /etc/fstab
# /etc/fstab: static file system information.
#
# Use 'blkid' to print the universally unique identifier for a
# device; this may be used with UUID= as a more robust way to name devices
# that works even if disks are added and removed. See fstab(5).
#
# <file system> <mount point>   <type>  <options>       <dump>  <pass>
# / was on /dev/sda1 during installation
UUID=f0591345-e04f-4a4a-a8b9-41c96e32fc99 /               ext4    errors=remount-ro 0       1
# swap was on /dev/sda5 during installation
UUID=c9462e3f-f306-484e-b8b4-cf4a680fab87 none            swap    sw              0       0
/dev/fd0        /media/floppy0  auto    rw,user,noauto,exec,utf8 0       0


Moment of truth. Reboot.

Check your work

~$ sudo swapon --show
NAME      TYPE      SIZE USED PRIO
/dev/sda5 partition   2G   0B   -1
~$ sudo free -m
              total        used        free      shared  buff/cache   available
Mem:           1991          85        1586           3         320        1856
Swap:          2047           0        2047
~$ sudo lsblk
NAME   MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
fd0      2:0    1    4K  0 disk
sda      8:0    0  100G  0 disk
├─sda1   8:1    0   98G  0 part /
├─sda2   8:2    0    1K  0 part
└─sda5   8:5    0    2G  0 part [SWAP]
sr0     11:0    1 1024M  0 rom
~$ sudo df -Th
Filesystem     Type      Size  Used Avail Use% Mounted on
udev           devtmpfs  977M     0  977M   0% /dev
tmpfs          tmpfs     200M  3.2M  197M   2% /run
/dev/sda1      ext4       97G  1.8G   91G   2% /
tmpfs          tmpfs     996M     0  996M   0% /dev/shm
tmpfs          tmpfs     5.0M     0  5.0M   0% /run/lock
tmpfs          tmpfs     996M     0  996M   0% /sys/fs/cgroup
tmpfs          tmpfs     100K     0  100K   0% /run/lxcfs/controllers
tmpfs          tmpfs     200M     0  200M   0% /run/user/1000
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