I use a laptop with Ubuntu 8.10 installed at work. While running the some high process, the CPU temperature get really high and its automatically shutdown the system. This thing happen every 2 or 3 days and its really annoying. The syslog showed the following error message:
ACPI: Critical trip point
Critical temperature reached (100 C), shutting down.
If your memory or mistyping leaves you without the right password to get into an account on a Linux computer, there’s no need to reformat. You’ll just need to reboot into single user mode to reset it. Here’s how to do it on a typical Ubuntu machine with the GRUB bootloader:
- Reboot the machine.
- Press the ESC key while GRUB is loading to enter the menu.
- If there is a ‘recovery mode’ option, select it and press ‘b’ to boot into single user mode.
- Otherwise, the default boot configuration should be selected. Press ‘e’ to edit it.
- Highlight the line that begins with ‘kernel’. Press ‘e’ again to edit this line.
- At the end of the line, add an additional parameter: ‘single’. Hit return to make the change and press ‘b’ to boot.
The system should load into single user mode and you’ll be left at the command line automatically logged in as root. Type ‘passwd’ to change the root password or ‘passwd someuser’ to change the password for your “someuser” admin account.
Once your done, give the three finger salute, or enter ‘reboot’ to restart into your machine’s normal configuration.
That’s all there is to it. Now just make sure to write your password down on a post-it and shove it somewhere safe like under your keyboard.
[ Source: Hackzine.com ]
The steps are not too difficult but I did have to find a few places for information. Search on the forum turn up nothing on this subject so hopefully this HOWTO would be helpful to someone out there.
Note: This is not using the OSE version.
VirtualBox has a very good GUI running on the host to manage guest OS. However when running a server, we typically do not want to run X on it. Fortunately VirtualBox has commandline tools to manage guest systems. It also provides the VirtualBox Remote Desktop Protocol (VRDP) to allow connection to the guest remotely.
Clarification of terms used:
Host – refers to the machine we are trying to install VirtualBox.
Guest – the VirtualBox guest system that is setup on the host.
Remote – the PC that we are working on to connect to the host via SSH.
This setup was done on a fresh install of Ubuntu Server 8.04 with openssh-server installed.
All the following steps are done by SSH into the host from a remote (I’m using Windows for now).
Dual-booting with Ubuntu and Windows sometimes giving a problem with date and time in Ubuntu. This is a well-established problem when dual-booting, since Linux assumes the hardware clock represents UTC, whereas Windows assumes the hardware clock represents local time. Luckily Linux provides ways to change this to fix it.
If you go into your clock settings, I think you can select between setting the hardware as either UTC or local time. Try switching that, and then adjust the time and see if it “sticks.”
If not, you can do this via the commandline in Linux :-
- In Linux, set the date and time to what it currently is. For example if it’s 10:20am local time:
user@server:~$ sudo date -s 10:20
- Then update the hardware clock accordingly, and force this to be considered “localtime”:
user@server:~$ sudo /sbin/hwclock --systohc --localtime
- Check to make sure it looks right:
user@server:~$ sudo /sbin/hwclock --localtime
- Sync between hardware clock and system clock:
user@server:~$ sudo /sbin/hwclock --hctosys --localtime
Now Linux should consider the clock to be “localtime”, which should be identical to what Windows is doing. So after rebooting into Windows, the time should look right.
Hope that helps.
It is possible to create a “reverse” SSH Tunnel. The reverse tunnel will allow you to create an SSH Tunnel from your work computer to your home computer, for example, and then login to your work machine from your home machine even if your work firewall does not permit ssh traffic initiated from your home machine!
For this to work, an SSH Server must be installed on your work and home computer, and ssh (TCP port 22) must be allowed outbound from your work computer to your home computer.
Syntax: ssh -R remote_port:localhost:22 your_home_computer
At home, you would then run ssh -p 2048 localhost to log into your work computer via ssh.
Here is a script that you can run through the cron facility on your work system to make sure the reverse SSH Tunnel to your home system is up and running. It is useful in case the system is rebooted.
# $REMOTE_HOST is the name of the remote system
# $REMOTE_PORT is the remote port number that will be used to tunnel
# back to this system
# $COMMAND is the command used to create the reverse ssh tunnel
COMMAND=”ssh -q -N -R $REMOTE_PORT:localhost:22 $REMOTE_HOST”
# Is the tunnel up? Perform two tests:
# 1. Check for relevant process ($COMMAND)
pgrep -f -x “$COMMAND” > /dev/null 2>&1 || $COMMAND
# 2. Test tunnel by looking at “netstat” output on $REMOTE_HOST
ssh $REMOTE_HOST netstat -an | egrep “tcp.*:$REMOTE_PORT.*LISTEN” \
> /dev/null 2>&1
if [ $? -ne 0 ] ; then
pkill -f -x “$COMMAND”
SSH Tunnelling is an excellent way to tunnel insecure protocols through a secure communication channel. In this example, I’ll tunnel POP3 traffic using SSH. Traditional POP3 traffic, including username and password information, travels clear-text across the network.
The syntax: ssh -f -N -L <local port>:<remote server>:<remote port> <userid>@<remote server>
To tunnel POP3 traffic using ssh:
- Make sure an ssh client is installed on your machine and an ssh server is installed on the POP3 server.
- Create a local SSH Tunnel on your machine (port 1234 for this example) to the POP3 server’s port 110. You will need to be the root user to bind to “privileged” ports (< 1024).
# ssh -f -N -L 1234:localhost:110 user@POP3_server
- Test the tunnel.
$ telnet localhost 1234
You should see the POP3 server’s banner information.est the tunnel.
- Configure your mail client to access your mail via POP3 using mail server localhost and port 1234.
After installing Ubuntu 7.10 there is no splash screen displayed at startup nor at shutdown. I just get a ‘Signal Out of Range’ message from my monitor.
A program called usplash controls this process, so I looked into it’s configuration, the values were totally off for my monitor, which uses a resolution of 1280 x 800.
By default the file looks like:
$ sudo cat /etc/usplash.conf
# Usplash configuration file
I edited the file:
$ sudo gedit /etc/usplash.conf
I changed the xres to: xres=1080 and the yres to: yres=800. Then I reconfigured the usplash program with the new settings.
$ sudo dpkg-reconfigure usplash
Problem fixed, now the splash image displays both at startup and shutdown.
Connecting two server running different type of SSH can be nightmare if you does not know how to convert the key. In this tutorial, I will try to explain on how to convert the public key from OpenSSH to SSH2 and SSH2 to OpenSSH. To convert the key, it must be done in OpenSSH server.
Convert OpenSSH key to SSH2 key
- Run the OpenSSH version of ssh-keygen on your OpenSSH public key to convert it into the format needed by SSH2 on the remote machine. This must be done on the system running OpenSSH.
#ssh-keygen -e -f ~/.ssh/id_dsa.pub > ~/.ssh/id_dsa_ssh2.pub
Convert SSH2 key to OpenSSH key
- Run the OpenSSH version of ssh-keygen on your ssh2 public key to convert it into the format needed by OpenSSH. This needs to be done on the system running OpenSSH.
#ssh-keygen -i -f ~/.ssh/id_dsa_1024_a.pub > ~/.ssh/id_dsa_1024_a_openssh.pub
This tutorial shows how to set up a Ubuntu Gutsy Gibbon (Ubuntu 7.10) based server that offers all services needed by ISPs and hosters: Apache web server (SSL-capable), Postfix mail server with SMTP-AUTH and TLS, BIND DNS server, Proftpd FTP server, MySQL server, Courier POP3/IMAP, Quota, Firewall, etc.
[ Source: HowtoForge ]