Archive for the ‘Bash’ Tag

Spanning files over multiple smaller devices   3 comments

Imagine you are in Tasmania and need to move 35TB (1 million files) to S3 in the Sydney region. The link between Tasmania and continental Australia will undergo maintenance in the next month, which means either one or both:

  • You cannot use network links to transfer the data
  • Tasmania might be drifting further away from the mainland now that it is untethered

In short, I’m going to be presented with a bunch of HDs and I need to copy the data on them, fly to Sydney and upload the data to S3. If the HD given would be 35TB I could just copy the data and be done with it – no dramas. Likely though, the HDs will be smaller than 35TB, so I need to look at a few options of doing that.

Things to consider are:

  • Files should be present on the HDs in their original form – so they can be uploaded to S3 directly without needing a staging space for unzipping etc
  • HDs should be accessible independently, in case a HD is faulty I can easily identify what files need copying again
  • Copy operation should be reproducible, so previous point could be satisfied if anything goes wrong in the copying process
  • Copying should be done in parallel (it’s 35TB, it’ll take a while)
  • It has to be simple to debug if things go wrong

LVM/ZFS over a few HDs

Building a larger volume over a few HDs require me to connect all HDs at the same time to a machine and if any of them fail I will lose all the data. I decide to not do that – too risky. It’ll also be difficult to debug if anything goes wrong.

tar | split

Not a bad option on its own. An archive can be built and split into parts, then the parts could be copied onto the detination HDs. But the lose of a single HD will prevent me from copying the files on the next HD.

tar also supports -L (tape length) and can potentially split the backup on its own without the use of split. Still, it’ll take a very long time to spool it to multiple HDs as it wouldn’t be able to do it in parallel. In addition, I’ll have to improvise something for untarring and uploading to S3 as I will have no staging area to untar those 35TB. I’ll need something along the lines of tar -O -xf ... | s3cmd.

tar also has an interesting of -L (tape length), which will split a volume to a few tapes. Can’t say I am super keen using it. It has to work the first time.

Span Files

I decided to write a utility that’ll do what I need since there’s only one chance of getting it right – it’s called It operates in three phases:

  • index – lists all files to be copied and their sizes
  • span – given a maximum size of a HD, iterate on the index and generate a list of files to be copied per HD
  • copy – produces rsync --files-from=list.X commands to run per HD. They can all be run in parallel if needed

The utility is available here:

I’ll let you know how it all went after I do the actual copy. I still wonder whether I forgot some things…


Posted February 7, 2016 by malkodan in System Administration

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Bloody Hell, Indent Your Scripts!!!   Leave a comment

Every so often I come across Bash scripts which are written as if Bash is a pile of rubbish and you just have to mould something ugly with it.

True, Bash is supposedly not the most “powerful” scripting language out there, but on the other hand if you’re using traditional methods then you can avoid installing gazillion ruby gems or perl/python modules (probably not even using RPM or DEB!!) just to configure your system. Bash is simple and can be elegant. But that’s not the point.

The point is that too often Bash scripts which people write have zero maintainability and readability. Why is that??

I’m not going to point at any bad examples because that’s not a very nice thing to do, although I can and easily.

Please do follow these three simple guidelines and you’ll get 90% of the job done in terms of maintainability and readability:

  • Functions – Write code in functions. Break your code into manageable pieces, like any other programming language, ey?
  • Avoid global variables – Global variables just make it all too complicated to follow what’s going on where. Sometimes they are needed but you can minimize the use of them.
  • INDENTATION – INDENT YOUR BLOODY CODE. If you have an if or for or what not, please just indent the block under it. It’s that simple and makes your code so much more readable.

That was my daily rant.

My Bash coding (or scripting) conventions cover a bit more and can be found here:

Handling many files in one directory   Leave a comment

The Assignment

You have a directory with gazillion files. Since most filesystems are not very efficient with many files in one directory, it is advisable to spread them among a hierarchy of directories. Write a program (or script) which handles a directory with many files and spreads them in an efficient hierarchy.

Does that sounds like a University assignment or something? Yes, it does.

Well apparently such a situation just happened to me in real life. Searching across the internet I couldn’t find anything too useful. And I will stand corrected if there is something which already deals with that problem. Post ahead if so.

And yes, thank god I’m using Unix (Linux), don’t even want to think what one would do on Windows.

The Situation

An application was spooling many files to the same directory, generating up to a million files in the same directory. I’m sorry I cannot disclose any more information about it, but lets just say it is a well known open source application.
Access to these files was obviously fast having ext4 and dir_index, but the directory index is too big to actually list files or do anything else without clogging everything in the system. And we need these files.

So we’ve decided to model the files in a way that’ll be more efficient for browsing and we can then handle it from there.

The Solution

After implementing something pretty quick and dirty for the situation, to mitigate the pain, I’ve sat down and wrote something a bit more generic. I’m happy to introduce the utility.
What does it take care of:

  • Reading the directory index just once
  • Hierarchy depth as parameter
  • Stacking up to X files per mv command
  • Has recursion in Bash!!
  • Obviously the best solution would be to never get to that situation, however if you do, feel free to use

SSHing efficiently   6 comments

I personally have a numerous number of hosts which I sometimes have to SSH to. It can get rather confusing and inefficient if you get lost among them.

I’m going to show you here how you can get your SSHing to be heaps more efficient with just 5 minutes of your time.


In $HOME/.ssh/config I usually store all my hosts in such a way:

Host host1
    Port 1234
    User root

Host host2
    Port 5678
    User root

Host host3
    Port 9012
    User root

You obviously got the idea. So if I’d like to ssh to host2, all I have to do is:

ssh host2

That will ssh to – saves a bit of time.

I usually manage all of my hosts in that file. Makes life simpler, even use git if you feel like it…

Auto complete

I’ve added to my .bashrc the following:

_ssh_hosts() {
    local cur="${COMP_WORDS[COMP_CWORD]}"
    local ssh_hosts=`grep ^Host ~/.ssh/config | cut -d' ' -f2 | xargs`
    [[ ! ${cur} == -* ]] && COMPREPLY=( $(compgen -W "${ssh_hosts}" -- ${cur}) )

complete -o bashdefault -o default -o nospace -F _ssh_hosts ssh 2>/dev/null \
    || complete -o default -o nospace -F _ssh_hosts ssh
complete -o bashdefault -o default -o nospace -F _ssh_hosts scp 2>/dev/null \
    || complete -o default -o nospace -F _ssh_hosts scp

Sweet. All that you have to do now is:

$ ssh TAB TAB
host1 host2 host3

We are a bit more efficient today.

Posted March 31, 2013 by malkodan in Bash, Linux, System Administration

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Bash Scripting Conventions   2 comments

Have decided to publish the infamous Bash scripting conventions.

Here they are:

Please, comment, challenge and help me modify it. I’m very open for feedback.

Posted January 28, 2013 by malkodan in Bash, Linux, System Administration

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Bash RPC   2 comments

Auto configuring complex cluster architectures is a task many of you might probably skip, using the excuse that it’s a one time task and it’ll never repeat itself. WRONG!
Being lazy as I could and the need to quickly deploy systems for hungry customers, I started out with a small little infrastructure that helped me along the way to auto configure clusters of two nodes or more.
My use cases were:
1. RedHat cluster
2. LVS
3. Heartbeat
4. Oracle RAC

Auto configuring an Oracle RAC DB is not an easy task at all. However, with the proper infrastructure, it can become noticeably easier.
The common denominators for all cluster configurations I had to carry were:
1. They had to run on more than one node
2. Except from entering a password once for all nodes, I didn’t want any interaction
3. They all consisted from steps that should either run on all nodes, or on just one node
4. Sometimes you could logically split the task into a few phases of configuration, making it easier to comprehend the tasks you have to achieve

Even though it is not the most tidy piece of Bash code I’m going to post here, I’m very proud of it as it saved me countless hours. I give you the skeleton of code, which is the essence of what I nicknamed Bash RPC. On top of this you should be able to easily auto configure various configurations involving more than one computer.

Using it

The sample attached is a simple script that should be able to bake /home/cake on all relevant nodes.
In order to use the script properly, edit it using your favorite editor and stroll through the configuration_vars() function. Populate the array HOST_IP with your relevant hosts.
Now you can simply run the script.
I’m aware to the slight disadvantage that you can’t have your configuration come from command line, on the other hand – when dealing with big, complex, do you really think your configuration can be defined in a single line of arguments?

Taming it

OK, this is the interesting part. Obviously no one needs to bake cakes on his nodes, it is truly pointless and was merely given as an example.
So how would you go about customizing this skeleton to your needs?
First and foremost, we must plan. Planning and designing is the key for every tech related activity you carry. Be it a SysAdmin task or a pure development task. While configuring your cluster for the first time, keep notes of the steps (and commands) you have to go through. Later on, try to logically separate the steps into phases. When you have them all, we can start hacking Bash RPC.
Start drawing your phases and steps, using functions in the form of PHASEx_STEPx.
Fill up your functions with your ideas and start testing! and that’s it!

How does it work?

Simplicity is the key for everything.
Bash RPC can be ran in 2 ways – either running all phases (full run) or running just one step.
If you give Bash RPC just one argument, it assumes it is a function you have to run. If no arguments are given it will run the whole script.
Have a look at run_function_on_node(). This function receives a node and functions it should run on. It will copy the script to the destination node and initiate it with the arguments it received.
And this is more or less the essence of Bash RPC. REALLY!

Oh, there’s one small thing. Sometimes you have to run things on just one host, in that case you can add a suffix of ___SINGLE_HOST for your steps. This will make sure the step will run on just one host (the first one you defined).

I’m more than aware that this skeleton of Bash RPC can be polished some more and indeed I have a list of TODOs for this skeleton. But all in all – I really think this one is a big time saver.

Real world use cases

I consider this script a success mainly because of 2 real world use cases.
The first one is the act of configuring from A to Z Oracle RAC. Those of you who had to go through this nightmare can testify that configuring Oracle RAC takes 2-3 days (modest estimation) of both a DBA and SysAdmin working closely together. How about an unattended script running in the background, notifying you 45 minutes later you have an Oracle RAC ready for service?

The second use case is my good friend and former colleague, Oren Held. Oren could easily take this skeleton and use it for auto configuring a totally different cluster using LVS over Heartbeat. He was even satisfied while using it. Oren never consulted me while performing this task – and this is the great achievement.

I hope you could use this code snippet and customize it for your own needs, continuing with the YOU CAN CREATE A SCRIPT FOR EVERYTHING attitude!!

Have a look at to get an idea about how it’s being done.

Posted October 10, 2009 by malkodan in Bash, Linux, System Administration

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Buying time   1 comment

Wearing both hats of developer and SysAdmin, I believe you shouldn’t work hard as a SysAdmin. It is for a reason that sometimes developers look at SysAdmins as inferior. It’s not because SysAdmins are really inferior, or has an easier job. I think it is mainly because a large portion of their workload could be automated. And if it can’t be automated (very little things), you should at least be able to do it quickly.

Obviously, we cannot buy time, but we can at least be efficient. In the following post I’ll introduce a few of my most useful aliases (or functions) I’d written and used in the last few years. Some of them are development related while the others could make you a happy SysAdmin.
You may find them childish – but trust me, sometimes the most childish alias is your best friend.

Jumping on the tree

Our subversion trunk really reminds me of a tree sometimes. The trunk is very thick, but it has many branches and eventually many leaves. While dealing with the leaves is rare, jumping on the branches is very common. Many times i have found myself typing a lot of ‘cd’ commands, where some are longer than others, repeatedly, just to get to a certain place. Here my stupid aliases come to help me.

lib takes me straight away to our libraries sub directory, where sim takes me to the simulators sub directory. Not to mention tr (shortcut for trunk), which takes me exactly to the sub directory where the sources are checked out. Oh, and pup which takes me to my puppet root, on my puppet master. Yes, I’m aware to the fact that you probably wonder now “Hey, is this guy going to teach me something new today? – Aliases are for babies!!”, I can identify. I didn’t come to teach you how to write aliases, I’m here to preach you to start using aliases. Ask yourself how many useful day-to-day aliases you really have defined. Do you have any at all? – Don’t be shy to answer no.

*nix jobs are diverse and heterogeneous, but let’s see if I can encourage you to write some useful aliases after all.
In case you need some ideas for aliases, run the following:

$ history | tr -s ' ' | cut -d' ' -f3- | sort | uniq -c | sort -n

Yes, this will show the count of the most recent commands you have used. Still not getting it? – OK, I’ll give you a hint, it should be similar to this:

$ alias recently_used_commands="history | tr -s ' ' | cut -d' ' -f3- | sort | uniq -c | sort -n"

If you did it – you’ve just kick-started your way to liberation. Enjoy.
As a dessert – my last childish alias:

$ alias rsrc='source ~/.bashrc'

Always useful if you want to re-source your .bashrc while working on some new aliases.

Two more things I must mention though:

  1. Enlarge your history size, I guess you can figure out alone how to do it.
  2. If you’re feeling generous – periodically collect the history files from your fellow team members (automatically of course, with another alias) and create aliases that will suit them too.

The serial SSHer

Our network is on Many times I’ve found myself issuing commands like:

$ ssh root@
$ ssh root@
$ ssh root@

Dozens of these in a single day. It was really frustrating. One day I decided to make an end to it:

# function for easier ssh
# $1 - network
# $2 - subnet
# $3 - host in subnet
_ssh_specific_network() {
	local network=$1; shift
	local subnet=$1; shift
	local host=$1; shift
	ssh root@$network.$subnet.$host

# easy ssh to
# $1 - host
_ssh_net_192_168_8() {
	local host=$1; shift
	_ssh_specific_network 192.168 8 $host
alias ssh8='_ssh_net_192_168_8'

Splendid, now I can run the following:

$ ssh8 1

Which is equal to:

$ ssh root@

Childish, but extremely efficient. Do it also for other commands you would like to use, such as ping, telnet, rdesktop and many others.

The cop

Using KDE’s konsole? – I really like DCOP, let’s add some spice to the above function, we’ll rename the session name to the host we’ll ssh to, and then restore the session name back after logging out:

# returns session name
_konsole_get_session_name() {
	# using dcop - obtain session name
	dcop $KONSOLE_DCOP_SESSION sessionName

# renames a konsole session
# $1 - session name
_konsole_rename_session_name() {
	local session_name=$1; shift
	_konsole_store_session_name `_konsole_get_session_name`
	dcop $KONSOLE_DCOP_SESSION renameSession "$session_name"

# store the current session name
_konsole_store_session_name() {

# restores session name
_konsole_restore_session_name() {
	if [ x"$STORED_SESSION_NAME" != x ]; then
		_konsole_rename_session_name "$STORED_SESSION_NAME"

# function for easier ssh
# $1 - network
# $2 - subnet
# $3 - host in subnet
_ssh_specific_network() {
	local network=$1; shift
	local subnet=$1; shift
	local host=$1; shift
	# rename the konsole session name
	_konsole_rename_session_name .$subnet.$host
	ssh root@$network.$subnet.$host
	# restore the konsole session name

Extend it as needed, this is only the tip of the iceberg! I can assure you that my aliases are much more complex than these.

Finders keepers

For the next one I’m not taking full credit – this one belongs to Uri Sivan – obviously one of the better developers I’ve met along the way.
Grepping cpp files is essential, many times I’ve found myself looking for a function reference on all of our cpp files.
The following usually does it:

$ find . -name "*.cpp" | xargs grep -H -r 'HomeCake'

But seriously, do I look like someone that likes to work hard?

# $* - string to grep
grepcpp() {
	local grep_string="$*";
	local filename=""
	find . -name "*.cpp" -exec grep -l "$grep_string" "{}" ";" | while read filename; do
		echo "=== $filename"
		grep -C 3 --color=AUTO "$grep_string" "$filename"
		echo ""

OK, let’s generalize it:

# grepping made easy, taken from the suri
# grepext - grep by extension
# $1 - extension of file
# $* - string to grep
_grepext() {
	local extension=$1; shift
	local grep_string="$*"
	local filename=""
	find . -name "*.${extension}" -exec grep -l "$grep_string" "{}" ";" | while read filename; do
		echo "=== $filename"
		grep -C 3 --color=AUTO "$grep_string" "$filename"
		echo ""

# meta generate the grepext functions
declare -r GREPEXT_EXTENSIONS="h c cpp spec vpj sh php html js"
_meta_generate_grepext_functions() {
	local tmp_grepext_functions=`mktemp`
	local extension=$1; shift
	for extension in $GREPEXT_EXTENSIONS; do
		echo "grep$extension() {" >> $tmp_grepext_functions
		echo '  local grep_string=$*' >> $tmp_grepext_functions
		echo '  _grepext '"$extension"' "$grep_string"' >> $tmp_grepext_functions
		echo "}" >> $tmp_grepext_functions
	source $tmp_grepext_functions
	rm -f $tmp_grepext_functions

After this, you have all of your C++/Bash/PHP/etc developers happy!

Time to showoff

My development environment is my theme park, here is my proof:

$ (env; declare -f; alias) | wc -l

I encourage you to run this as well, if my line count is small and I’m bragging about something I shouldn’t – let me know!

Posted August 21, 2009 by malkodan in Bash, Linux, System Administration

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