Lekensteyn's questions

I'm running the current stable Ubuntu version (Oneiric) but have issues with the shipped kernel. Newer kernel versions seem to have fixed it, but the kernel-ppa/ppa does not contain the most recent kernel which is why I want to install the kernel from the next stable version (Precise). Since I want to be able to unload out of tree kernel modules, the mainline kernel from http://kernel.ubuntu.com/~kernel-ppa/mainline cannot be used.

I also have have Virtual Box installed which also need to work in the new kernel so the "kernel headers" have to be upgraded as well.

How am I supposed to install the kernel packages from the next stable version (Precise) without upgrading all other packages?

The powertop program shows the power usage, but only after about five minutes. Before that, it shows:

no ACPI power usage estimate available

That's one of the limitations of the powertop program. What program is recommended for reliably monitoring the power usage? Is it possible to get a power usage history similar to the memory usage history in the System Monitor as well?

I've recorded a video using recordmydesktop, but have unfortunately chosen for capturing the whole screen (1600*896) instead of a small part with geometric 900*690.

How do I crop this video? Preferably in the editor I'm using, Kdenlive, to minimize quality loss. I've tried the Crop, Pan & Zoom and Scale0tilt effects, modifying the pixel ratio, movie size inside project settings options without success. A step-by-step guide would be preferred or at least some hints.

From the technical overview of Ubuntu 11.10 Oneiric:

Ubuntu 11.10 has migrated away from /var/run, /var/lock and /dev/shm and now uses /run, /run/lock and /run/shm instead (respectively).

• I hardcode these paths in my applications, why is this change made to Oneiric?
• What can I do to make my applications backwards- and forward-compatible? Is there a better way other than checking first for the existence of /run, and then /var/run?

I just switched from the Konversation IRC client to the terminal based IRSSI. I'm starting IRSSI on a remote machine using GNU screen + SSH. I do not get any sound notification on new messages, which means that I've to check out IRSSI once in a while for new messages.

That's not really productive, so I'm looking for an application / script that plays a sound (preferably /usr/share/sounds/KDE-Im-Irc-Event.ogg and not the annoying beep) on my machine if there is any activity. It would be great if I can disable the notification for certain channels.

Or, if that's not possible, some sort of notification via libnotify, thus making it available to GNOME and KDE.

Sometimes, a graphical text editor like gedit or kate cannot be used (because you're in a virtual console for example). Luckily, there are text editors for the terminal. An easy one is nano, but I cannot understand how to work with it.

If I start nano by running nano, the bottom text is supposed to help me but all I see are things like ^G Get Help ^O WriteOut.

1. How can I open text files for editing?
2. How can I save the file?
3. How can I quit the editor without saving the changes?
4. How to edit? I heard that you've to enter some commands to begin editing in vi, is this true for nano too?
5. Sometimes, if I manage to open a file, the text is unreadable due to its colors. How can I disable these colors? (see the image below)
6. In the some files, lines are truncated because those do not fit in the screen. How can I prevent that from happening? (see the image below)

A SSH private key as generated by ssh-keygen contains a public key part. How do I retrieve this public key from the private key? I've lost my public key and need to put the contents of this public key in the servers authorized_keys file and do not want to create a new key pair.

Alternatively phrased: how do I create the id_rsa.pub file from a id_rsa file?

Following the instructions in Best way to cache apt downloads on a LAN?, I've set up a caching proxy in my local network. Since that machine is not always up, I'd like to be able to refresh the sources list and install packages without using that proxy if unavailable.

I've already read the Acquire group section in the manual page of apt.conf(5), but I couldn't find an option like "Silent-Fail".

At the moment, sudo apt-get update and related commands fail because no connection could be established. So how do I configure the client so that the proxy is ignored if it's not available?

I've RPM file of which I want to examine its file contents. For .deb packages, I can use dpkg -x file.deb to extract it.

What is the equivalent command for a .rpm file? I'm looking for a command-line application.

ssh-agent is very easy to use, I start it and add keys using ssh-add keyfile. After killing the process ssh-agent, all files are gone.

How can I get the same behavior with gpg-agent? The closest program I found was gpg-preset-passphrase. But looking at the manual page of gpg-agent, it seems that a directory is created for storing private keys.

I could be wrong, so I'm wondering how I can setup gpg-agent in such a way that no files/ directories are created? If it's not possible, other suggestions to make gpg-agent work like ssh-agent + ssh-add would be welcome too. I'm not looking for GUI solutions like Seahorse.

ændrük suggested a reverse connection for getting an easy SSH connection with someone else (for remote help). For that to work, an additional user is needed to accept the connection. This user needs to be able to forward his port through the server (the server acts as proxy).

How do I create a restricted user that can do nothing more than the above described?

The new user must not be able to:

• execute shell commands
• access files or upload files to the server
• use the server as proxy (e.g. webproxy)
• access local services which were otherwise not publicly accessible due to a firewall
• kill the server

Summarized, how do I create a restricted SSH user which is only able to connect to the SSH server without privileges, so I can connect through that connection with his computer?

For helping others quickly, SSH is very useful, especially combined with GNU Screen. It's common that users are behind a NAT router. Even if the user can configure the router, it takes some time to remember the password, find the right options, etc.

So, what is the easiest way to help others over SSH if they're behind a NAT router?

I currently tell people to open a terminal run the below command and pass me their IP from a site like http://ip.appspot.com/:

sudo apt-get install openssh-server ssh-import-id && ssh-import-id lekensteyn

Obviously, this is not going to work if they're behind a NAT router or have a personal firewall configured. So, is there something like:

sshd --accept-help-from lekensteyn

I'm not looking for alternatives like Teamviewer, just a shell like SSH. It should be open-source too.

I believe that umask is something that controls file permissions, but do not fully understand it.

After running umask 0644 in a terminal, I cannot read the files I create with the command-line text editor nano. I noticed that the permissions of that file are set to 0022 instead of the default 0755.

How does umask work? I thought I could just remove the each digit in the umask from 0777, 7 - 6 = 1 and 7 - 4 = 3, so I expect the permissions to be 0133, but apparently, this is not the case.

1. What is umask exactly? Explain it to me like I was a "Linux noob"
2. How do I calculate with umask?
3. What are use cases for umask?

I've just received my new SSD since the old one died. This Intel 320 SSD supports TRIM. For testing purposes, my dealer put Windows on it, but I want to get rid of this and install Kubuntu on it.

It does not have to be a "secure wipe", I just need the empty the disk in the most healthy way. I believe that dd if=/dev/zero of=/dev/sda just fills the blocks with zeroes and thereby taking another write (correct me if I'm wrong).

I've seen the answer How to enable TRIM, but it looks like it's suited for clearing empty blocks, not wiping the disk.

hdparm seems to be the program to do it, but I'm not sure if it clears the disk OR cleans empty blocks. From its manual page:

  --trim-sector-ranges
          For  Solid State Drives (SSDs).  EXCEPTIONALLY DANGEROUS. DO NOT
          USE THIS OPTION!!  Tells the drive firmware to discard  unneeded
          data  sectors,  destroying  any  data that may have been present
          within them.  This makes those sectors available  for  immediate
          use  by  the firmware's garbage collection mechanism, to improve
          scheduling for wear-leveling of the flash  media.   This  option
          expects  one  or  more  sector range pairs immediately after the
          option: an LBA starting address, a colon, and  a  sector  count,
          with no intervening spaces.  EXCEPTIONALLY DANGEROUS. DO NOT USE
          THIS OPTION!!

          E.g.  hdparm --trim-sector-ranges 1000:4 7894:16 /dev/sdz

How can I make all blocks appear as empty using TRIM?

Duplicity does already a great job of making efficient backups, but I want still to minimize the amount of files being back-upped.

What files or directories can be excluded in a home directory? Please name these explicitly, wildcards allowed, paths are relative to the home directory.

For a smooth upgrade from 10.04 to 10.10, I would like to remove all packages which are not in the default repositories (e.g. chromium PPA and third-party repositories). What is the easiest way (preferably CLI) to find and remove these packages?

Edit: this question is not restricted to PPA's, I have a x2go repository as well, so I'm looking for a generic command to remove packages belonging to a certain repository. For PPA's, the question How can PPAs be removed has great answers.

As you can see in the changelog for the Linux kernel, there are update messages like "Bump ABI - Maverick ABI 28".

According to the Ubuntu Wiki, ABI is something like a bridge between the kernel space and the other modules (my interpretation).

Does such an update adds extra features and / or bugfixes? Should I upgrade my kernel to the next version?

I am often interested in the installation triggers (postinst, postrm) or certain parts of packages (like /usr/share and /etc). Currently, I am running the next command to retrieve the source code:

apt-get source [package-name]

The downside is, this file is often much bigger than the binary package and does not reflect the installation tree.

Right now, I am downloading the packages through http://packages.ubuntu.com/:

1. Search for [package-name]
2. Select the package
3. Click on amd64/i386 for download
4. Download the actual file

This takes too long for me and as someone who really likes the shell, I would like to do something like the next (imaginary) command:

apt-get get-deb-file [package-name]

I could not find something like this in the apt-get manual page. The most close I found was the --download-only switch, but this puts the package in /var/cache/apt/archives (which requires root permissions) and not in the current directory.

I have seen the answer on How to disable hibernating?, but I have no such file. Possibly because that suggestion was written for Ubuntu, not Kubuntu (KDE, not Gnome).

I do not have a swap on my encrypted SSD, my system freezes (cannot even change Caps Lock) if I accidentally press the "Hibernate" button at "Energy management". My keyboard has a Hibernate button (Fn + F4) next to the volume control buttons and every time I press the wrong key, the system will freeze after.

So, what is the correct way to disable it? If there is no solution, a work-around is welcome too.

I've two interfaces: eth0 and wlan0 on a notebook.

Possible use cases:

• eth0 grants me Internet access, and wlan0 is currently connected to a router which does not have Internet-connectivity. For development purposes, I need to connect to the wlan0 by default, but use eth0 for surfing
• eth0 and wlan0 are both connected to the Internet. For a torrent application, eth0 should be used for speed, but for portability of the notebook, SSH should have a connection over wlan0
• eth0 is a wire connection, wlan0 is a wireless one. Sensible data should be transferred over eth0, but other traffic can go over wlan0 as well.

Is there a way to force applications (like nc.traditional or firefox) to use a certain network interface? A wrapper like example-wrapper eth0 program is fine too if such program exist. It would be nice if it could configured within Firefox (in runtime). I'd like to avoid IPTables solutions if possible.