How to log history and logins from multiple ssh-keys under one user account

Many times your managed server has only one user account into wich every admin logs in with his personal ssh-key. Most times it’s done with the root account, but that’s a nother topic 😉 As a result of this behaviour your are not able to see who logged in and what he or she did. A often suggested solution would be using different user account per person with only one ssh-key for authorization. This adds the „overhead“ of memorizing (except when you use ~/.ssh/config) and managing the sudoers file for all the accounts.

A more clever way is to use the SSH Environment feature in your authorized_keys file. First you need to enable this feature within the /etc/sshd/sshd_config file:

PermitUserEnvironment yes

After that you can configure your ~/.ssh/authorized_keys file:

environment="SSH_USER=USER1" ssh-rsa AAAAfgds...
environment="SSH_USER=USER2" ssh-rsa AAAAukde..

This sets the SSH_USER variable on Login in reference to the used ssh-key. NOw that this variable is updated on every login you can go on and work with it. First of to the logging of the actuall key that logs in. Under normal circumstances the ssh-dameon logs only the following information

sshd[21169]: Accepted publickey for user_account from 127.0.0.1 port 46416 ssh2

Additinally you could pass the SSH_USER content on to the syslog-dameon to log the actual user:

if [ "$SSH_USER" != "" ]; then
  logger -ip auth.notice -t sshd "Accepted publickey for $SSH_USER"
fi

This writes the following into the /var/log/auth (Debian) or /var/log/messages (RedHat) file:

sshd[21205]: Accepted publickey for USER1

Further more you can change the bash history file to a personal user file:

  export HISTFILE="$HOME/.history_$SSH_USER"

 

All together it looks like this:

if [ "$SSH_USER" != "" ]; then
  logger -ip auth.notice -t sshd "Accepted publickey for $SSH_USER"
  export HISTFILE="$HOME/.history_$SSH_USER"
fi

 

Puppet
To use the environment option within your ssh-key management in puppet you need the options field from the ssh_authorized_key function:

ssh_authorized_key { "${username}":
 
  key     =>  "AAAAsdnvslibyLSBSDFbSIewe2131sadasd...",
  type    =>  "ssh-rsa,
  name    =>  "${username}",
  options =>  ["environment=\"SSH_USER=${username}\""],
  user    =>  $user,
  ensure  =>  "present",
}

 

Hope this helps, have fun! :)

p.s.: This is a guest post by Martin Mörner, a colleague from Aperto.

Using backuppc as a dirty distributed shell

Backuppc is a neat server-based backup solution. In Linux envorinments it is often used in combination with rsync over ssh – and, let’s be hontest – often fairly lazy sudo or root rights for the rsync over ssh connection. This has a lot of disadvantages, but at least, you can use this setup as a cheap distributed shell, as a good maintained backuppc server might have access to a lot of your servers.

I wrote a small wrapper, that reads the (especially Debian/Ubuntu packaged) backuppc configuration and iterates through the hosts, allowing you to issue commands on every valid connection. I used it so far for listing used ssh keys, os patch levels and even small system manipulations.

1
2
3
4
5
6
7
8
9
10
11
12
13
14
#!/bin/bash
SSH_KEY="-i /var/lib/backuppc/.ssh/id_rsa"
SSH_LOGINS=( `grep "root" /etc/backuppc/hosts | \
 awk '{print "root@"$1" "}' | \
 sed ':a;N;$!ba;s/\n//g'` )
 
for SSH_LOGIN in "${SSH_LOGINS[@]}"
do
 HOST=`echo "${SSH_LOGIN}" | awk -F"@" '{print $2'}`
 echo "--------------------------------------------"
 echo "checking host: ${HOST}"
 ssh -C -qq -o "NumberOfPasswordPrompts=0" \
 -o "PasswordAuthentication=no" ${SSH_KEY} ${SSH_LOGIN} "$1"
done

You can easily change this to your needs (e.g. changing login user, adding sudo and so on).

$ ./exec_remote_command.sh "date"
--------------------------------------------
checking host: a.b.com
Mo 9. Mai 15:40:26 CEST 2011
--------------------------------------------
checking host: b.b.com
[...]

Make sure to quote your command, especially when using commands with options, so the script can handle the command line as one argument.

A younger sister of the script is the following ssh key checker that lists and sorts the ssh keys used on systems by their key comment (feel free to include the key itself):

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
#!/bin/bash
 
SSH_KEY="-i /var/lib/backuppc/.ssh/id_rsa"
SSH_LOGINS=( `grep "root" /etc/backuppc/hosts | \
 awk '{print "root@"$1" "}' | \
 sed ':a;N;$!ba;s/\n//g'` )
 
for SSH_LOGIN in "${SSH_LOGINS[@]}"
do
 HOST=`echo "${SSH_LOGIN}" | awk -F"@" '{print $2'}`
 echo "--------------------------------------------"
 echo "checking host: ${HOST}"
 ssh -C -qq -o "NumberOfPasswordPrompts=0" \
 -o "PasswordAuthentication=no" ${SSH_KEY} ${SSH_LOGIN} \
 "cut -d: -f6 /etc/passwd | xargs -i{} egrep -s \
 '^ssh-' {}/.ssh/authorized_keys {}/.ssh/authorized_keys2" | \
 cut -f 3- -d " " | sort
 ssh -C -qq -o "NumberOfPasswordPrompts=0" \
 -o "PasswordAuthentication=no" ${SSH_KEY} ${SSH_LOGIN} \
 "egrep -s '^ssh-' /etc/skel/.ssh/authorized_keys \
 /etc/skel/.ssh/authorized_keys2" | cut -f 3- -d " " | sort
done

A sample output of the script:

$ ./check_keys.sh 2>/dev/null
--------------------------------------------
checking host: a.b.com
[email protected] 
[email protected]
some random key comment
--------------------------------------------
checking host: b.b.com
[...]

That’s all for now. Don’t blame me for doing it this way – I am only the messenger :)

Having fun with OpenSSH on Ubuntu Intrepid Ibex – visual host keys

After having a quite uneventful upgrade to Ubuntu Intrepid Ibex (time for a change), I’s happy to notice, that Intrepid Ibex ships the new OpenSSH version 5.1 which has one little feature, I really fell in love with: visual host keys. You might already have read about it on Planet Ubuntu. In case you don’t: „visual host keys“ is a way presenting the ssh client user a 2d ascii art visualation of the host key fingerprint. It shall help you to recognize a ssh server by remembering a figure rather than the host key.

If you want to give this a try, call the ssh client this way:

$ ssh -o VisualHostKey=yes your.host.name
Host key fingerprint is ff:aa:a8:dc:0b:5e:e3:9f:96:f1:75:d4:24
+--[ RSA 1024]----+
|            +o   |
|             o. .|
|            E  + |
|       .   . .. .|
|      . S   ..   |
|   . o o..  . .  |
|    + + .+.. .   |
|   . + ooo.      |
|    . ooo        |
+-----------------+

Nice, isn’t it? Now try your different ssh hosts and compare the figures. Hope you don’t start generating ssh host keys for getting a special figure, do you? :) Actually I don’t know if I’ll really remember figures of dozens of machines, but hey: it’s just additional fun.

In case you want to make this behavior default, add „VisualHostKey yes“ to your „~/.ssh/config“. In case you don’t have this file, make a new one with the following content (and find out that this file makes ssh really poweful in combination with command line completion, but that is another topic):

Host *
	VisualHostKey		yes

Please note: This might break applications that rely on the ssh console client as they don’t expect graphical art popping up. So if some other clients don’t work anymore, play around with aliases or your ~/ssh/config file.

Thank you, OpenSSH guys, I really appreciate your work.

my package of the day – gpg for symmetric encryption

Though asymmetric encryption is state of the art today, there are still cases when you probably are in need of a simple symmetric encryption. In my case, I need an easy scriptable interface for encrypting files for backup as transparent as possible. While you can, of course, use asymmetric encryption for this, symmetric methods can save you a lot of time while still being secure enough.

So there are methods like stupid .zip encryption or a bunch of packages in the repositories like „bcrypt“ that provide you with their implementations. But there is a tool, you already know and maybe even use, but don’t think of when considering symmetric encryption: „gpg„. Actually gpg heavily relies on symmetric algorithms as you might know. The public/private key encryption is a combination of asymmetric and symmetric encryption as the latter is quite more cpu efficient. In our case, gpg will use the strong cast5 cipher by default.

Encrypting

So as gpg already knows about a bunch of symmetric encryption algorithms, why not use them? Let’s just see an example. You have a file named „secretfile1.txt“ and want to encrypt it:

$ gpg --symmetric secretfile1.txt

You will be prompted for a password. Afterwards you’ll have a file named secretfile1.txt.gpg. You are already done! Please note: The file size of the encrypted file might have decreased as gpg also compresses during encryption and outputs a binary. In my test case the file size went down from 700k to 100k. Nice.

Armoring

In case you need to have an easy portable file that is even ready to be copy-pasted, you can ask gpg to create an ascii armor container:

$ gpg --armor --symmetric secretfile1.txt

The output file will be called „secretfile1.txt.asc“. Don’t bother to open it in a text editor of your choice. The beginning will look similar to this:

$ head secretfile1.txt.asc
-----BEGIN PGP MESSAGE-----
Version: GnuPG v1.4.6 (GNU/Linux)

jA0EAwMChpQrAA/o8IFgye1j3ErZPvXumcnIwbzSvENDD/fYlWMRiY/qqvn949kV
+mo/v+nQi7OFrrA45scQPuPbj8I1T+2f7XAT4ouW2kuHIJ/2zkyrxBMvO04fDH82
273NwUrXd/s+JJXe+wJz149K324rE7+FIHvfImiez8lRs5qyRI/drp/wFK8ZHRvF
gzhDGaTe8Dgj1YqHgWAY4eAjrXhYLI1imbIYrV1OVPia6Roif37FV7C1AT/i/2HX
2ytI2mBhQLdqkSVeqXZ74lgZhsitnOeqZH65IuTLi77PUcroFOuefw6+4qSpMIuM
8dyi4jCqQ1jCR7PRorpGvm3RtXhlkB689vrknKmOa5uztTj3MGrPOgC6jegBpu/L
3419sAxRtw8bj2lP76B+XXPZ2Tuzpg01hC/BWlifSexy+juYXv7iuF5BuQ1z7nTi

(In this case I used ‚head“ for displaying the first ten lines. Head is similar to tail, which you might already know.) Though the ascii file is larger than the binary .gpg file it is still much smaller than the original text file (about 200k in the above case). When tampering with binary files like already compressed tarballs the file size of the encrypted file might slightly increase. In my test, the size grew from a 478kB file to a 479kB file when using binary mode. In ascii armor mode the size nearly hit the 650kb mark, which is still pretty acceptable.

Decrypting

Decrypting is as easy. Just call „gpg –decrypt“, for instance:

$ gpg --decrypt secretfile1.txt.gpg
# or
$ gpg --decrypt secretfile1.txt.asc

gpg knows by itself, if it is given an ascii armored or binary file. But nevertheless the output will be written to standard output, so the following line might be much more helpful for you:

$ gpg --output secretfile1.txt --decrypt secretfile1.txt.gpg

Please note, that you need to stick to the order first –output, then –decrypt. Of course you can also use a redirector („>“).

Piping

So, for the sake of it: The real interesting thing is that you can use gpg symmetric encryption in a chain of programs, controlled by pipes. This enables you to encrypt/decrypt on the fly with shell scripts helping you to write strong backup scripts. Gpg already detects, if your are using it in a pipe. So let’s try it out:

$ tar c directory | gpg --symmetric --passphrase secretmantra \
| ssh hostname "cat > backup.tar.gpg"

We just made a tarbal, encrypted it and sent it over ssh without creating temporary files. Nice, isn’t it? To be honest, piping over ssh is not a big deal anymore. But piping to ftp? Check this:

$  tar c directory | gpg --symmetric --passphrase SECRETMANTRA \
| curl --netrc-optional --silent --show-error --upload-file - \
--ftp-create-dirs ftp://USER:PASSWORD@SECRETHOST/SECRETFILE.tar.gpg

With the mighty curl we just piped from tar over gpg directly to a file on a ftp server without any temporary files. You might get a clue of the power of this chain. Now you can start using a dumb ftp server as encrypted backup device now completely transparently.

That’s all for now. If you like encryption, you should also check symmetric encryption and the possibilities of enhancing daily business scripts security by adding some strong crypto to it. Of course you can complain about the security of the password, the possible visibility via „ps aux“, but you should be able to reduce risks by putting some brain in it. In the meantime check „bashup„, the bash backup script, which uses methods described here to provide you with a powerful and scriptable backup library written in Bash with minimum depencies. And yes, gpg will be added soon.

my package of the day – sash – the Stand Alone SHell for system recovery

Let me introduce you today to a package that is quite unknown as you hopefully never need it. But when you need it and have not thought about it before, it is probably already too late. I am talking about „sash“ – the „Stand Alone SHell“. Yet another shell? Yes and no. Yes it is a shell, but no, I am not trying to show something like the shiny friendly interactive shell or (my favorite) „zsh“. Quite the contrary: You can give „sash“ a lot of attributes, but not „shiny“.

So what is about? Imagine the following case: You are running a machine and suddenly something goes totally wrong. Partition errors, missing libraries, you have messed around with libc, whatever. This can get you into serious trouble. You are fine, when you have the possibility to boot a recovery cd or something similar. But under some circumstances you might have to stick to the programs already installed though they seem to be broken. Maybe it is a virtual server somewhere on the web and you are only allowed to boot into a recovery mode giving you a prompt to your server. So you are trying to login as root but it just does not work for some reasons. Broken dependencies. Who knows.

The point is: When you login onto a machine for system recovery, you are already relying on a lot of tools and dependencies – though it only seems to be a shell. The shell might be linked against a couple of libraries, a lot of commands you want to run are not build in and therefore a bunch of external dependencies can bar your way. So what you actually might need in a situation of severe pain is a shell that provides you with as much essential tools as you need on its own without relying on external code.

Installing sash

This is where „sash“ comes into play. Sash is not a dynamic linked executable, it has actually all needed features built in. So as long as you can execute the sash binary, you can have a working shell. Let’s check it! Install „sash“ by using „aptitude install sash“ or you preferred package manager. Please note, that sash will clone your current root account:

cloning root account entry to create sashroot account in /etc/passwd
Cloned sashroot from root in /etc/passwd
cloning root account entry to create sashroot account in /etc/shadow
Cloned sashroot from root in /etc/shadow

So you have this new line in your /etc/passwd:

sashroot:x:0:0:root:/root:/bin/sash

You should consider giving sashroot a password if you want to be able to login with this account. But please check if this applies to your security needs.

See the difference

Now let’s check how the sash binary differs from the standard shell, the bash and the zsh. We are using „ldd“ for this, as it is lists libraries, an executable is linked against:

bildschirmfoto-terminal.png

Pretty impressive. All „normal“ shells have at least three dependencies, sash apparently has none.

But getting rid of external libraries is not the only difference sash makes. Another major feature is the collection of built-in commands:

-ar, -chattr, -chgrp, -chmod, -chown, -cmp, -cp,
-dd, -echo, -ed, -grep, -file, -find, -gunzip,
-gzip, -kill, -ln, -ls, -lsattr, -mkdir, -mknod,
-more, -mount, -mv, -printenv, -pwd, -rm, -rmdir,
-sum, -sync, -tar, -touch, -umount, -where

Seems like a list of commands you yearn for, when in recovery mode, don’t you? Note the leading „-“ at the beginning of those commands. This is the way, sash handles your attempts to run internal and external commands. When using „mv“, sash gives you the normal /bin/mv, when using „-mv“, sash provides you with it’s own replacement. But „sash“ helps you when you don’t want to type the „-“ at the beginning of every command. You can enter „aliasall“ in a sash session as it will create non permanent aliases for all builtin commands:

bildschirmfoto-terminal-1.png

Emergency

In case of an emergency you might need to boot directly into sash as maybe your initrd stuff is broken. How? Just append a „init=/bin/sash“ to your kernel command line – be it lilo or grub. This way, you will be directly dropped into a sash session.

What’s missing?

Sadfully one essential command is missing: fsck. As the sash manual points out: fsck is just way too big to be included in a statically linked binary. Sad, but true. But hey: Better being to able at least to act on the console than having no console at all.

Sash as a standard shell?

… is not a good idea. It just lacks a lot of features you’ll really want when working on the command line: A verbose prompt, command history, tab completion and so on.

So it’s to install sash now as you will miss it, when it’s too late :)
(And just if you’d like to ask: Yes, at least once I really needed sash and it helped me to save a lot of time.)

my package of the day: proggyfonts – tiny fonts for programmers and console users

(Well, it is not yet a package, but trust me: I’ll make sure it gets one.)

As a programmer or console user you might know the pain of having not as much characters on you screen as you would like to. You tried around with different fonts, it got better by reducing font size but it is not yet perfect. If I tell you, that you just have the wrong fonts you probably moan „… I tried all installed fonts“. And you are right by that: The fonts I am going to tell you about are definitely not preinstalled.

I ran into the font trouble a couple of years ago. As my eyes are quite good I yearned for a really tiny font to overflow my brain with as much content as possible on the same time. After I a while I started a research on the web and found a page that already sounds like a perfect hit: proggyfonts.com. The site hosts 24 monospaced bitmap programming fonts (licensed under a free BSD-type personal license) enhanced for a small screen footprint and issues that programmers often run into like differing 0 (zero) from O (capital letter „o“).

Font comparison

The font I use is called „ProggyFont Tiny Slashed Zero“ which stands for: A real tiny font with a cleary slashed zero. To compare it to a „normal“ font let’s see it in action. Here you can see a default installed Monospace font which has been set up to a small font size:

bildschirmfoto-mc-hasung-mnt-cryptdevice-live-home-ccm.png

Concentrate on the characters you see above: They blur a bit. It’s not a big deal but if you are working with it for hours it gets one. Now let’s compare the same screen with ProggyFont Tiny Slashed Zero:

bildschirmfoto-mc-hasung-mnt-cryptdevice-live-home-ccm-1.png

See how clear the characters are? It even got smaller – you could handle one or two lines more within the same space if you would resize the window according to the previous one. What a relief!

Even more fonts

Now the example given is the most aggressive one as it is really small. You might consider other fonts as helpfull. Let me give you another example of a font: Proggy Clean (better to read as it is bigger) Slashed Zero Bold Punc – see yourself:

font.png

What have they done? They assume when you are a programmer you like characters like brackets, colons and so on being bold as the mean something in the code. Often you have to deal with interfaces that don’t mark those characters. Now the font does this for you. Nice, isn’t it? Now even cat and less show you bold coding elements without even configuring them to do so.

Installation

The site hosts the fonts in different formats. As I am lazy and is supported I only use the TTF font. To enroll a font in Gnome you have two ways depending on your Gnome version. First download a font package, unzip it, so you have file named fontname.ttf. To speak in Ubuntu versions: If you running Ubuntu Gutsy or below, open Nautilus, go to „fonts:///“ and drag and drop the ttf file into it and just restart your X session. If you have Hardy, create a directory called „.fonts“ in your home directory and copy the ttf file into it. Restart X afterwards (though not all applications depend on this).

Now open the application you want to enhace with your shiny new font. Let’s say it’s gnome-terminal. You should be able to choose a font named ProggySomething. Now you have to choose a font size and that is the only tricky thing to do: You have to find out the only possible font size. This setting might differ from application to application. In gnome-termin it is „11“ for instance which seems huge, but in fact is not. Just try it out. Under KDE or even Windows/OSX you’ll find out fast how to enroll the fonts. In fact it works, you just have to try.

So now you have a new set of fonts ready to boost your productivity. Make sure you don’t get a headache when using it and don’t crash your brain with an information overflow. I’ll report back when I packaged those fonts for a simple usage in Debian/Ubuntu.

my package of the day: fish – the friendly interactive shell

Always wanted to learn using a shell more deeply? Maybe „fish„, the „friendly interactive shell“ is the right kickoff for you.

If you are already a heavy command line user with customized .bashrc or even .zshrc (like me), thank you probably don’t need another shell. But if this shell thingy is somehow a miracle to you but you saw people using it like wizards with colorful commands and a typing speed that made you jealous then it could help you to start with a shell that concentrates on being very friendly to new users as common shells like Bash and ZSH expect you to read the manual and write a config file (there are aids and defaults that vary from distribution to distribution).

The standard shell for login users in Ubuntu/Debian is „Bash“. Ubuntu already ships the file /etc/bash_completion that is read by default and helps users using the TAB key more exensively. Try it on you bash shell: just type something like „ls –“ and press TAB twice. You’ll see a list of options that „ls“ provides. Nice but it could be nicer. Let’s compare this to fish. Install fish by using Synaptic or „aptitude install fish“, open a terminal and start the shell by typing „fish“. You should a changed green prompt. Now type „ls -“ and press TAB.

Stop: Already while typing you should see a strange color change. When entering „l“ the character turns red and underlined. Looks like an error? Well, it is: fish tells you, that „l“ is probably not a command. An aid during typing before running a command. Neat. Now, when pressing TAB you should a very clean list of options for „ls“ with a short description of each option:

fish11.png

Helpfull, isn’t it? Of course this is not limited to ls. Try it with other commands you are using. If you ask yourself why you have to type „command –“ and press TAB: „–“ introduces a command line option („-“ does this also – try it!). As you press TAB after this, the shells knows „the user wants to do something and needs help on completing it“. It looks after a pattern and sees that you want to use the given command and are looking for options. That’s all. As I said: This works in Bash often by default also, but not that nice.

Now fish can do more with completion of course. Want to install a program? Try „aptitude install mut“ and press TAB. It will show you a list of packages matching that pattern:

fish2.png

Need to kill a process? Type „kill “ and press TAB and you will get a nice list of running processes:

fish3.png

The list of possible TAB completions on fish is endless. Just notice that emphasis has been put on commands like mount, make, su, ssh, apt-get/aptitude. In most commands usernames, process ids will automatically be completed. The trick is just to try TAB when you are too lazy to type or unsure how to proceed. A good shell surprises you from time to time with it’s completion.

Also very helpful is the extended pattern matching for file names. Let’s say you want a list of all pdf files in a directory and all it’s subdirectories. On bash you probably use something like „find . -name „*.mp3“. On fish you use the pattern „**“ which means any files and directories in the current directory and all of its subdirectories. So type „ls **.pdf“ and you get the list you want as fish crawls through the directories for you. Want alle .mp3 and mp4 files but not files like .mpeg? Use „ls **.mp?“ as „?“ stands for one character. Of course commands like „rm **.bak“ are possible, too. Use them with care! In the following example we are looking for pdf files in all subdirectorie, delete them and afterwards make sure they are really gone:

bildschirmfoto-fish-mnt-cryptdevice-live-home-ccm-work-1.png

So let me stop here. I hope, I was able to show you that using fish instead of an unconfigured shell is a nice way of getting in the command line business. Fish provides you with a lot of more features that you might need and saves you from writing a config file from scratch.

If you want to give fish a try: Install it and run the „help“ command. I will launch a nice help page in you browser. Read some parts of the document as they’ll show you nice gimmicks. Or just don’t and start right away. But trust me: Reading hints for a shell from time to time will save you … time.

(Just in case you don’t know: You can change your standard shell by using the „chsh“ command. But when being a novice it is always a good idea to stick to the distribution specific default shell and run your shell directly by calling it. When you are more used to it feel free to make it your standard shell…)

removing outdated ssh fingerprints from known_hosts with sed or … ssh-keygen

At least from the last issue in Debian-based systems including Ubuntu you might know the pain of getting the message from you ssh client that the server host key has changed as ssh stores the fingerprint of ssh daemons it connects to. Actually this is a neat feature because it helps you detecting man in the middle attacks, dns issues and other things you probably should notice.

Until recently I opened the file .ssh/known_hosts in vim, deleted the entry, saved the file and started over again. I randomly checked „man ssh“ which gives you a lot of hints about the usage of known_hosts but I just did not find information about how to delete an old fingerprint or even overwrite it. I imagined something like „ssh –update-fingerpring hostname“ with an interactive yes/no question you cannot skip. There is the setting „StrictHostKeyChecking“ that might get you out of the fingerprint-has-changed-trouble but it does not solve the real problem as you want those checks.

So after hanging around with Mnemonikk discussing this he pointed out a very simple method with „sed“ that is really handy and helps you understanding sed more deeply. You can advise „sed“ to run a command on a specific line. So have a look at this session:

1
2
3
4
5
6
7
8
9
10
11
12
13
14
$ ssh secrethost
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
@    WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED!     @
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY!
[...]
Offending key in /home/ccm/.ssh/known_hosts:46
[...]
Host key verification failed.
$ sed -i "46 d" .ssh/known_hosts
$ ssh secrethost
The authenticity of host 'secrethost (1.2.3.4)' can't be established.
RSA key fingerprint is ab:cd:ef:ab:cd:ef:ab:cd:ef:ab:cd:ef:ab:cd:ef:ab.
Are you sure you want to continue connecting (yes/no)?

We just took the line number 46 which ssh complains about and run in in-place-editing mode (-i) with the command run on line 46 the command delete (d). That was easy, wasn’t it? Small lesson learned about sed. Thank you Mnemonikk (he is currently working on a screencast about screen if you let me leak some information here :).

But to be honest I’s still looking for the „official“ method the delete a key from known_hosts. Therefore I browsed through the man pages and finally found what I was looking for in „man ssh-keygen“. Yes, definitely zero points for usability as deleting with a tool named „generator“ is confusing but it works, however. You can advice ssh-keygen to delete (-R) fingerprints for a hostname which helps you when you turned hashed hostnames on in you known_hosts:

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
$ ssh secrethost
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
@    WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED!     @
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
[...]
Offending key in /home/ccm/.ssh/known_hosts:63
[...]
Host key verification failed.
[ccm@hasung:255:/etc/ssh]$ ssh-keygen -R secrethost
/home/ccm/.ssh/known_hosts updated.
Original contents retained as /home/ccm/.ssh/known_hosts.old
[ccm@hasung:0:/etc/ssh]$ ssh secrethost
The authenticity of host 'secrethost (1.2.3.4)' can't be established.
RSA key fingerprint is ab:cd:ef:ab:cd:ef:ab:cd:ef:ab:cd:ef:ab:cd:ef:ab.
Are you sure you want to continue connecting (yes/no)?

So „ssh-keygen -R hostname“ is a nice syntax as you even do not have to provide the file name and path for known_hosts and it works with hashed names. Nevertheless I’ll also use the sed syntax – keep it trained it’ll help you in other cases also.

Bashup – a first example for a simple tree backup over ssh

Some days (weeks?) ago I told you about the release of „Bashup“ a bourne shell compatible backup script on sourceforge. As the script is still in heave Alpha I’d like to give you a first insight into it’s development.

Bashup is written in heavy Bash syntax and has few dependencies to external programs. You should image it as a scripting library for backups as it allows to call different backup methods and is more a framework than a fully integrated solution. The power of this is the ability to be free in the creation of a backup process while still using easy methods.

The following is a fairly easy setup of bashup for backing up some directories over ssh. You see that we only source the bashup library here, setup some variables and call the bashup method then which executes the backup.

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
#!/bin/bash
# source bashup lob
. bashup_lib.sh
 
# set setup source - we want to backup a tree
SOURCE=tree
# set source dirs
TREE_DIRECTORIES="$HOME/PDF $HOME/ogg"
# setup filter for compression
FILTER=bzip2
 
# set destination - we want to ssh
DESTINATION=ssh_file
# set ssh host, you could be clever
# and setup access in .ssh/config
SSH_HOST=host.name.tld
# set remote file name
FILE=file.name.bz2
 
# we want two types of logging
USE_REPORTERS="console log"
 
# set the log file names
COMBINED_LOG=combined.log
ERROR_LOG=error.log
 
# call bashup
bashup

I admit this example won’t win a Noble award but if you are busy with setting up backups on very different servers you might like the idea of a scripting environment which only needs bash. Imagine your power when digging deeper into the bashup lib and calling the special methods directly while piping output and more. This is possible of course.

In the next weeks I’ll show you how to use backup rotation (yes, also over ssh, ftp and other methods), mysql/postresql/oracle/subversion backup, nagios feedback integration and more.

If you like to test and tell me what you think or even want to provide patches, feel free to checkout bashup:

svn co https://bashup.svn.sourceforge.net/svnroot/bashup bashup

Bashup – a sophisticated Bash backup script

Mnemonikk (who still lacks a blog because he cannot decide which name to choose) finally made the step to create a sourceforge project for Bashup. Bashup is a more or less modular and Bourne shell compatible backup script with few dependencies. It targets backup for servers and provides features like mysql, oracle, postgresql, subversion repository and file system backup, backup over ftp, ssh, rsync, heavy rotation (yes – even over ftp) and reporting. The script is already used on a couple of different live servers. It matches the need for a script that is neither binary, nor python, ruby or perl but just plain shell and some external calls.

The script is released under GPL. Right now you can only get it by checking out the svn repository (see sourceforge project page for details) but will be branched with an official version number soon. I know there are a lot of backup solutions out there and this is just one more, but you might also know how difficult it can be to backup a system when having very limited possibilities to install software and servers distributed on very different data centers…

Feel free to contact me for gaining access as developer. Patches and new modules welcome!