Get your data together!

Analyzing logs is fun, kind of like how going to the dentists is fun. You stair at lon-n-n-n-g pages of data and your brain goes numb from the overwhelming amount of information.

GBT is a Perl script that can condense and extract meaningful information from time-indexed logs and numbers. GBT is Group-By-Time and rather than have sporadic bursts of data separated by black holes of emptiness, GBT produces a consistent flow of data that is easily graphable 

GBT by default will condense data into ten minute blocks of maximum values for each column given. The size of the time block can be changed using the -t argument. The output data format can be changed to provide min, max, mean, sum, delta or count. 

The main use for GBT is to pipe data into GNU Plot to produce graphs.

GBT hosted on GitLab.com

Here is the gnuplot PNG created from the sample data.

Ooooh that shell, Can't you shell that shell

Staying up late to work on a fun project. Building a custom PXE boot image that will be used to pre-load our servers and get them ready for Puppet management. It has been about eight years since I had built a custom boot image. At that time busybox was my goto for small, powerful environments that needed to run from very small RAM mounted file systems.

BusyBox combines tiny versions of many common UNIX utilities into a single small executable. It provides replacements for most of the utilities you usually find in GNU fileutils, shellutils, etc. The utilities in BusyBox generally have fewer options than their full-featured GNU cousins; however, the options that are included provide the expected functionality and behave very much like their GNU counterparts. BusyBox provides a fairly complete environment for any small or embedded system.

When most distros offer boot images that do little more than boot, or fail to boot; for my systems I used busybox to create a very compact environment that would allow you to perform diagnostics and fix any problems.

As great as busybox was at the time, I found it lacked a lot of compatibilities with even old POSIX systems and scripts. Arguments that you rely on for find, grep and even ls, just were not there. Things have changed; somewhat. Busybox has grown up and is full of new abilities.

Screenshot of "make menuconf" providing the ability
to choose the features to build into the binary.

The ancestry of a process

When it comes to viewing the heritage of a process, the go-to command is pstree. By itself, pstree will show the descendant processes. Using the -s argument it will show ancestor processes. A good trick to remember is slap, pstree -slap <PID>.

I personally like the format of ps and being the kind of person that likes to come up with one line tools, I created this little snippet.

{ TPID=$$; while [[ $TPID -ne 1 ]]; do ps -f $TPID | tail -n1; TPID=$(ps h -o ppid -p $TPID); done; ps -f $TPID|tac; } | tac

Saving it to use later we get this.

#!/bin/bash

{ 
        TPID=${1:-$$}; 
        while [[ $TPID -ne 1 ]]; do 
                ps -f $TPID | tail -n1; 
                TPID=$(ps h -o ppid -p $TPID); 
        done; 
        ps -f $TPID | tac; 
} | tac

This is what the two commands output.

Jget, a simple CLI web client for testing

“Knock, knock.”
“Who’s there?”
very long pause….
“Java.”

I made this to test the way Java makes web requests. It is both simple and inefficient at being a web client.

/*  Compile
 *  javac Jget.java
 *
 *  Testing
 *  java Jget http://google.com
 */

import java.io.*; 
import java.net.*;  

public class Jget {  
 public static String getHTML(String urlToRead) throws Exception { 
  StringBuilder result = new StringBuilder(); 
  URL url = new URL(urlToRead); 
  HttpURLConnection conn = (HttpURLConnection) url.openConnection(); 
  conn.setRequestMethod("GET"); 
  BufferedReader rd = new BufferedReader(new InputStreamReader(conn.getInputStream())); 
  String line; 
  while ((line = rd.readLine()) != null) { 
   result.append(line); 
  } 
  rd.close(); 
  return result.toString(); 
 }  

 public static void main(String[] args) throws Exception { 
  System.out.println(getHTML(args[0])); 
 } 
}

Expandable Disk Server

In my SOHO I have tried many types of storage solutions. Currently the system is a Qnap, four bay system. It's turn key, user friendly approach does make it easy to setup and use, but it's highly limited with not having a fifth drive bay. Four bays allows for two disks in RAID-1 or one big disk in RAID-10, not having a fifth bay prevents upgrading to larger disks, without fronting the cash to buy an entire new system and disks all at once.

It's time for a storage solution that can grow over time, not only to replace smaller disk but to allow for the system to start with just one disk and add to the cluster over the next few month.

Looking at using FreeNAS to manage a NAS server built from a Linux box. This will not be a dedicated box, so I will be building a Proxmox and hosting the FreeNAS as a VM inside the Proxmox. The FreeNAS needs to grow as new disks are added so it will be using the disks as an NFS share from Proxmox.

The plan is to use Wester Digital 12TB disks, as these disks are almost $700 each, only one disk will be added to the system every two weeks over the next two months.

Building the disk array will use Linux software RAID-1, LVM, and XFS.

RAID-1
This level of RAID is for redundancy, all disks in the RAID are kept identical. When one disk fails the file system continues to work.

LVM
LVM visualises the block layer of block devices. This is a powerful tool for manipulating block devices on a running system. LVM does have builtin support for mirroring and RAID, including RAID-1 and RAID-10, but happens at the logical volume layer and using these would prevent the migration to larger disks.

XFS
This file system allows for growing live without the need to format or reboot the system.

To test this plan, and demonstrate how this will work, VMware running Fedora 27 was used. The images used a 8GB SCSI for the root file system. The disks in the cluster are SATA and are marked a through f.

In this example the commands used create Physical Volumes with names that match the RAID-1 device, while the images show the Physical Volumes with PV names.

Step 1 Create a new RAID-1
mdadm --create /dev/md0 --run --level=1 --raid-devices=2 /dev/sda missing

Step 2 Create a new physical volume
pvcreate /dev/md0

Step 3 Create a new volume group
vgcreate vg0 /dev/md0

Step 4 Create a new logical volume
lvcreate -l 100%VG -n lv0 vg0

Step 5 Create the XFS
mkfs.xfs /dev/vg0/lv0
mkdir /xfs0
mount /dev/vg0/lv0 /xfs0/

Step 6 Add another disk to the RAID
mdadm --add /dev/md0 /dev/sdb

Step 7 Create a new RAID-1
mdadm --create /dev/md1 --run --level=1 --raid-devices=2 /dev/sdc missing

Step 8 Create a new physical volume
pvcreate /dev/md1

Step 9 Grow the existing volume group
vgextend vg0 /dev/md1

Step 10 Grow the existing logical volume
lvextend -l 100%VG vg0/lv0

Step 11 Grow the existing XFS live
xfs_growfs /xfs0/

Add the last disk the same way as Step 6.



Expand the disk cluster by adding new PVs and migrating

Step 12 Create the new RAID and PV
mdadm --create /dev/md2 --run --level=1 --raid-devices=2 /dev/sd/ missing
pvcreate /dev/md2

Step 13 Extend the volume group to include the new PV
vgextend vg0 /dev/md2

Step 14 Move all blocks from the old PV to the new PV.
pvmove /dev/md0 /dev/md2

Step 15 Remove the first PV.
vgreduce vg0 /dev/md0

Step 16 Grow the logial volume again
lvextend -l 100%VG vg0/lv0

Step 17 Re-grow the existing XFS live
xfs_growfs /xfs0/

Now on GitLab.com

You can now download all the code from GitLab.com

git clone git@gitlab.com:SiliconTao-open-source/linux-code-snippets.git

Host your projects on GitLab.com

Sed: Append file to end of line

Sed can let you replace part of a line with new content from another file. This is how I do this in three steps. You can see the code run a codingground

By using a file to insert the replacement text the content can contain special characters that would normally require a lot of extra work to escape. 

#!/bin/bash

# Replace the right portion of a line with the content of a file.
# 1) Replace the right portion of a line with a marker word
# 2) Append after the marker with the content from a file
# 3) Remove the marker and new line to pull the next line up.

cat > outfile <<!EOF
hello there tom
        How are you today?
    Where is the dog show?
!EOF

cat outfile

cat > testfile <<!EOF
flowers doing?
!EOF


sed -i outfile -e 's/you.*/REPLACE_MARKER/g'
printf "\n\n\n"
cat outfile

sed -i outfile -e "/REPLACE_MARKER/r testfile"
printf "\n\n\n"
cat outfile

sed -i outfile -e "/REPLACE_MARKER/{:a;N;s/REPLACE_MARKER\n//}"
printf "\n\n\n"
cat outfile