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All the Operation Engineers and SREs that work with systems have found the situation of having a Server with the disk full of logs and needing to keep those logs, and at the same time needing the system to keep running.
This is an uncomfortable situation.
I remember when I was being interviewed in Facebook, in Menlo Park, for a SDM position in the SRE (Software Development Manager) back in 2013-2014. They asked me about a situation where they have the Server disk full, and they deleted a big log file from Apache, but the space didn’t come back. They told me that nobody ever was able to solve this.
I explained that what happened is that Apache still had the fd (file descriptor), and that he will try to write to end of that file, even if they removed the huge log file with rm command, from the system they will not get back any free space. I explained that the easiest solution was to stop apache. They agreed and asked me how we could do the same without restarting the Webserver and I said that manipulating the file descriptors under /proc. They told me what I was the first person to solve this.
How it works
Basically cmemgzip will read a file, as binary, and will load it completely in to Memory.
Then it will compress it also in Memory. Then it will release the memory used to keep the original, will validate write permissions on the folder, will check that the compressed file is smaller than the original, and will delete the original and, using the new space now available in disk, write the compressed and smaller version of the file in gzip format.
Since version 0.3 you can specify an amount of memory that you will use for the blocks of data read from the file, so you can limit greatly the memory usage and compress files much more bigger than the amount of memory.
If for whatever reason the gz version cannot be written to disk, you’ll be asked for another route.
I mentioned before about File Descriptors, and programs that may keep those files open.
So my advice here, is that if you have to compress Apache logs or logs from a multi-thread program, and disk is full, and several instances may be trying to write to the log file: to stop Apache service if you can, and then run cmemgzip. I want to add it the future to auto-release open fd, but this is delicate and requires a lot of time to make sure it will be reliable in all the circumstances and will obey the exact desires of the SRE realizing the operation, without unexpected undesired side effects. It can be implemented with a new parameter, so the SysAdmin will know what is requesting.
Get the source code
You can decompress it later with gzip/gunzip.
So about cmemgzip you can git clone the project from here:
git clone https://gitlab.com/carles.mateo/cmemgzip
The README.md is very clear:
The program is written in Python 3, and I gave it License MIT, so you can use it and the Open Source really with Freedom.
Do you want to test in other platforms?
This is a version 0.3.
I have only tested it in:
- Ubuntu 20.04 LTS Linux for x64
- Ubuntu 20.04 LTS 64 bits under Raspberry Pi 4 (ARM Processors)
- Windows 10 Professional x64
- Mac OS X
It should work in all the platforms supporting Python, but if you want to contribute testing for other platforms, like Windows 32 bit, Solaris or BSD, let me know.
You can create a ramdisk and compress it to there. Then delete the original and move the compressed file from ramdisk to the hard drive, and unload the ramdrive Kernel Module. However we find very often with this problems in Docker containers or in instances that don’t have the Kernel module installed. Is much more easier to run cmemgzip.
Another strategy you can do for the future is to have a folder based on ZFS and compression. Again, ZFS should be installed on the system, and this doesn’t happen with Docker containers.
cmemgzip is designed to work when there is no free space, if there is free space, you should use gzip command.
In a real emergency when you don’t have enough RAM, neither disk space, neither the possibility to send the log files to another server to be compressed there, you could stop using the swap, and fdisk the swap partition to be a ext4 Linux format, format it, mount is, and use the space to compress the files. And after moving the files compressed to the original folder, fdisk the old swap partition to change type to Swap again, and enable swap again (swapon).
As you can imagine, the weak point of cmemgzip, is that, if the file is completely loaded into memory and then compressed, the requirements of free memory on the Server/Instance/VM are at least the sum of the size of the file plus the sum of the size of the file compressed. You guess right. That’s true.
If there is not enough memory for loading the file in memory, the program is interrupted gracefully.
I decided to keep it simple, but this can be an option for the future.
So if your VM has 2GB of Available Memory, you will be able to use cmemgzip in uncompressed log files around 1.7GB.
In version 0.3 I implemented the ability to load chunks of the original file, and compress into memory, so I would be able use less memory. But then the compression is less efficient and initial tests point that I’ll have to keep a separate file for each compressed chunk. So I will need to created a uncompress tool as well, when now is completely compatible with gzip/gunzip, zcat, the file extractor from Ubuntu, etc…
For a big Server with a logfile of 40TB, around 300GB of RAM should be sufficient (the Servers I use have 768 GB of RAM normally).
Honestly, nowadays we find ourselves more frequently with VMs or Instances in the Cloud with small drives (10 to 15GB) and enough Available RAM, rather than Servers with huge mount points. This kind of instances, which means scaling horizontally, makes more difficult to have NFS Servers were we can move those logs, for security.
So cmemgzip covers very well some specific cases, while is not useful for all the scenarios.
I think it’s safe to say it covers 95% of the scenarios I’ve found in the past 7 years.
cmemgzip will not help you if you run out inodes.
Usage is very simple, and I kept it very verbose as the nature of the work is Operations, Engineers need to know what is going on.
I return error level/exit code 0 if everything goes well or 1 on errors.
./cmemgzip.py /home/carles/test_extract/SherlockHolmes.txt cmemgzip.py v.0.1 Verifying access to: /home/carles/test_extract/SherlockHolmes.txt Size of file: /home/carles/test_extract/SherlockHolmes.txt is 553KB (567,291 bytes) Reading file: /home/carles/test_extract/SherlockHolmes.txt (567,291 bytes) to memory. 567,291 bytes loaded. Compressing to Memory with maximum compression level… Size compressed: 204KB (209,733 bytes). 36.97% of the original file Attempting to create the gzip file empty to ensure write permissions Deleting the original file to get free space Writing compressed file /home/carles/test_extract/SherlockHolmes.txt.gz Verifying space written match size of compressed file in Memory Write verification completed.
You can also simulate, without actually delete or write to disk, just in order to know what will be the
There are no third party libraries to install. I only use the standard ones: os, sys, gzip
So clone it with git in your preferred folder and just create a symbolic link with your favorite name:
sudo ln --symbolic /home/carles/code/cmemgzip/cmemgzip.py /usr/bin/cmemgzip
I like to create the link without the .py extension.
This way you can invoke the program from anywhere by just typing: cmemgzip
So you are trying to program the Raspberry expansion PINS in Python, for example for this 3D LED Christmas Tree, and you’re getting the error:
GPIO.setup(self.number, GPIO.IN, self.GPIO_PULL_UPS[self._pull])
RuntimeError: Not running on a RPi!
I’m running this on Ubuntu 20.04LTS with a Raspberry 4.
The first thing:
Make sure you have an official Raspberry Pi charger.
Or at least, make sure your USB charger provides enough intensity to power the Raspberry and the LEDs.
The LED power comes from the motherboard and if Raspberry Pi has not enough energy this is not going to work.
My colleague Michela had her tree not working because of the charger was not able to provide enough energy. When she ordered a new charger, it worked like a charm.
Install the base Software
In order to communicate with General Purpose Input Output ports (GPIO) you need to install this Software:
sudo apt install python3-pip python3-gpiozero sudo pip3 install giozero
In order to run the 3D LED Christmas Tree code samples
sudo pip3 install colorzero sudo pip3 install rpi.gpio --upgrade
It may be not required in some cases.
Download the Source code
Run the samples as root
I saw many people stuck, in the forums, because of that.
To work with the LEDs you need to run the samples as root.
Where I used it?
I used it in my Open Source monitor Software CTOP.py in order to show the plugins/extensions capability of it. :)
- I have updated CTOP.py so now it detects if is running in a Google GCP instance.
So the list of instances/type of virtualization detected is:
- Amazon AWS
- Google GCP
- Docker containers
I’m working in detecting Raspberry Pi, models running CTOP, and in enabling the plugins system so anybody can easily expand the functionality of ctop.py.
Commented annotations and type hinting, to make CTOP compatible with Python 3.5.0.
Added Available RAM.
Added Google GCP detection.
Inform if it doesn't have permissions to decode DMI.
Print the userId (numeric) and the User (string), like: 1000 carles or 0 root.
Logic for swappiness <= 10 Ok, >10 and <= 30 warning, >30 red (alert).
Reduced digits for swap to 2, to avoid confusions.
- I have updated my book Python 3 Combat Guide, with another full cycle, step by step, to convert an ugly script that escapes to shell to a nice OOP code with Unit Testing, step by step.
- I have updated my book ZFS for Ubuntu 20.04 LTS, adding how to create a pool and Datasets for home, sharing NFS for the Media Player.
- If you like Star Wars and the Mandalorian, you may laugh has much as I did with this video:
- I continue teaching programming classes to some people, Pyhon and Java.
- I’ve contribute to this article about what is DevOps in plain words.
- The latest articles are about:
- Oracle: Fix ORA600 [KGL-heap-size-exceeded]
- Fixing Wifi disabled in Dell laptops and Kali Linux as my colleagues, students, were experiencing this.
- Helping the Community:
- Solving Windows 10 PRO running Active Directory as Domain Admin when initiated session as a different user.
- Install Windows Subsystem for Linux, WSL 2 on Windows 10 64 bit, with Ubuntu, solution to error WslRegisterDistribution failed with error: 0x80070057
As you see I’m writing more articles about Windows, Mac Os X, and proprietary Software. Some of my colleagues work in companies and use proprietary Software, so I’ll be writing more articles about those ecosystems. I spend more time now with colleagues working on all kind of projects, and with students that have other problems too, so I help them. However my main focus is Open Source, Architecture, Scaling, programming in Python and Java.
Time ago there was a web page that was rendered in blank for certain group of users.
The errors were coming from an Oracle instance. One SysAdmin restarted the instance, but the errors continued.
Often there are problems due to having two different worlds: Development and Production/Operations.
What works in Development, or even in Docker, may not work at Scale in Production.
That query that works with 100,000 products, may not work with 10,000,000.
I have programmed a lot for web, so when I saw a blank page I knew it was an internal error as the headers sent by the Web Server indicated 500. DBAs were seeing elevated number of errors in one of the Servers.
So I went straight to the Oracle’s logs for that Servers.
I did a quick filter in bash:
cat /u01/app/oracle/diag/rdbms/world7c/world7c2/alert/log.xml | grep "ERR" -B4 -A3
This returned several errors of the kind “ORA 600 [ipc_recreate_que_2]” but this was not the error our bad guy was:
‘ORA 600 [KGL-heap-size-exceeded]’
The XML fragment was similar to this:
<msg time='2016-01-24T13:28:33.263+00:00' org_id='oracle' comp_id='rdbms' msg_id='7725874800' type='INCIDENT_ERROR' group='Generic Internal Error' level='1' host_id='gotham.world7c.justice.cat' host_addr='10.100.100.30' pid='281279' prob_key='ORA 600 [KGL-heap-size-exceeded]' downstream_comp='LIBCACHE' errid='726175' detail_path='/u01/app/oracle/diag/rdbms/world7c/world7c2/trace/world7c2_ora_281279.trc'> <txt>Errors in file /u01/app/oracle/diag/rdbms/world7c/world7c2/trace/world7c2_ora_281279.trc (incident=726175): ORA-00600: internal error code, arguments: [KGL-heap-size-exceeded], [0x14D22C0C30], , , , , , , , , ,  </txt></msg>
Just before this error, there was an error with a Query, and the PID matched, so it seemed cleared to me that the query was causing the crash at Oracle level.
Checking the file:
The content was something like this:
<msg time='2016-01-24T13:28:33.263+00:00' org_id='oracle' comp_id='rdbms' msg_id='7725874800' type='INCIDENT_ERROR' group='Generic Internal Error' level='1' host_id='gotham.world7c.justice.cat' host_addr='10.100.100.30' pid='281279' prob_key='ORA 600 [KGL-heap-size-exceeded]' downstream_comp='LIBCACHE' errid='726175' detail_path='/u01/app/oracle/diag/rdbms/world7c/world7c2/trace/world7c2_ora_281279.trc'> <txt>Errors in file /u01/app/oracle/diag/rdbms/world7c/world7c2/trace/world7c2_ora_281279.trc (incident=726175): ORA-00600: internal error code, arguments: [KGL-heap-size-exceeded], [0x14D22C0C30], , , , , , , , , ,  </txt> </msg>
Basically in our case, the query that was launched by the BackEnd was using more memory than allowed, which caused Oracle to kill it.
That is a tunnable that you can modify introduced in Oracle 10g.
You can see the current values first:
SQL> select 2 nam.ksppinm NAME, 3 nam.ksppdesc DESCRIPTION, 4 val.KSPPSTVL 5 from 6 x$ksppi nam, 7 x$ksppsv val 8 where nam.indx = val.indx and nam.ksppinm like '%kgl_large_heap_%_threshold%'; NAME | DESCRIPTION | KSPPSTVL ============================================================================================= _kgl_large_heap_warning_threshold | maximum heap size before KGL | 4194304 writes warnings to the alert log --------------------------------------------------------------------------------------------- _kgl_large_heap_assert_threshold | maximum heap size before KGL | 4194304 raises an internal error
So, _kgl_large_heap_warning_threshold is the maximum heap before getting a warning, and _kgl_large_heap_assert_threshold is the maximum heap before getting the error.
Depending in your case the solution can be either:
- Breaking your query in several to reduce the memory used
- Use paginating or LIMIT
- Set a bigger value for those tunnables.
It will work setting 0 for these to variables, although I don’t recommend it to you, as you want your Server to kill queries that are taking more memory than you want.
To increase the value of , you have to update it. Please note it is in bytes, so for 32MB is 32 * 1024 * 1024, so 33,554,432, and using spfile:
SQL> alter system set "_kgl_large_heap_warning_threshold"=33554432 scope=spfile ; SQL> shutdown immediate SQL> startup SQL> show parameter _kgl_large_heap_warning_threshold NAME TYPE VALUE ==================================|=========|=============== _kgl_large_heap_warning_threshold | integer | 33554432
Or if using the parameter file, set:
This is a trick I share, as I see many students having problems with this.
Assuming that your Kali distribution is recent (Linux Kernel bigger than Kernel 5.3), the most typical problem student have is that laptops xps from Dell and other brands have a combination of keys to enable or disable the Wifi.
On the Dell xps is on the key PrtScr, so if your Wifi is disabled, you can enable it in Kali Linux press:
CTRL + ALT + Fn + PrtScr
As you can see in the PrtScr the is an icon of Wifi Signal.
The Fn key is on the bottom left, next to Ctrl.
This is a very simple to fix problem, but many people suffer this problem and go crazy trying to update drivers or even having to use an external USB dongle.
This is an answer that I did to a question in askubuntu.
I have one HDD formatted as single disc zfs system on my server. It looks like the following:
Now I want to convert this to a zfs mirror without formatting the original disk. Any ideas?
Result should be something like:
hdd0 mirror0 ata-........................ ata-........................
I reproduced your case in a VM and paste here step by step. :)
Note: First of all, please do a backup of your data. I added an empty new disk, so ZFS had no doubt what was the master drive. Although you should have no problem as the first drive already forms part of the pool, a backup is recommended.
Quick answer: You need the zpool attach command.
And you will see that a mirror has been created. Your data on the already existing drive will be keep, and will be replicated to the new one (Resilvered).
As ZFS only copys the actual information this process will take more or less depending on the amount of Data.
In my VM 300 GB were replicated in 3 seconds, while my experience with SAS and SATA drives, I was Resilvering 10 TB in less than 24 hours (for that I was using drives from 10TB to 14TB SAS) .
Now the long answer with everything I did in my Virtual Box VM:
identify the two empty drives by:
Select one of them and create a pool like your: sudo zpool create hdd0 id_of_mydrive
See that pool /hdd0 has been created and mounted on root.
Fill with some random data (or better copy files there) to generate a drive like data like you. I generated from random:
|sudo dd id=/dev/urandom of=/hdd0/file.000 bs=1M count=100 status=progress |
sudo dd id=/dev/urandom of=/hdd0/file.001 bs=1M count=100 status=progress
sudo dd id=/dev/urandom of=/hdd0/file.002 bs=1M count=100 status=progress
Then I got the checksum and saved to verify later.
zpool list shows nearly 100GB of space.
zpool status will show:
pool: hdd0 state: ONLINE scan: resilvered 301M in 0 days 00:00:03 with 0 errors…
NAME STATE READ WRITE CKSUM
ata-VBOX_HARDDISK_VBa8... ONLINE 0 0 0
ata-VBOX_HARDDISK_VB8c... ONLINE 0 0 0errors: No known data errors
I verified the checksums.
zpool list will return as well 99GB of space available, as two drives of 100GB are being used in mirror.
So as kaulex mentioned the format is: zpool attach
Where device is your previous vdev with data (the single hard drive with Data in the ZFS pool named ‘hdd0’).
As I did you want to use the Id of the device and not the name, so you will use the identifier in /dev/disk/by-id/ and not sdb, sdc… (Please note, adding /dev/ is not necessary). The reason to do not use device names like sdb, sdc, sdea, etc… is that those names may change why live is running or between reboots. The id never changes. In real systems, not Virtual Box, they may start by wwn or ata.
I’ve been helping to troubleshoot the reason one Commodity Server (with no iDrac/Ilo ipmi) is powering off randomly. One of the hypothesis is the temperature.
This is a very simple script that will print the temperature of the HDDs and the CPU and keep to a log file.
First you need to install hddtemp and lm-sensors:
sudo apt install hddtemp lm-sensors
Then this is the one line script, that you should execute as root:
while [ true ]; do date | tee -a /var/log/hddtemp.log; hddtemp /dev/sda /dev/sdb /dev/sdc /dev/sdd | tee -a /var/log/hddtemp.log; date | tee -a /var/log/cputemp.log; sensors | tee -a /var/log/cputemp.log; sleep 2; done
Feel free to change sleep 2 for the number of seconds you want to wait, like sleep 10.
Press CTRL + C to interrupt the script at any time.
You can execute this inside a screen session and leave it running in Background.
Note that I use tee command, so the output is print to the screen and to the log file.
This explains how to solve a problem if you logged in to the domain, via your computer, as a regular user, and then you need to run Active Directory with Administrator privileges as another user.
First open CMD.exe as Administrator.
C:\WINDOWS\system32>runas /netonly /user:mydomain\carles.adm "mmc.exe dsa.msc /server=myserver.mydomain.com"
Assuming my regular user is: carles
And my Administrator user is: carles.adm
You know I love Linux. I was compiling my own Kernels back in 1995, when it took more than 24 hours in a 386, and working on the first ISPs in Barcelona managing the Linux Systems.
For my computers I prefer Linux, no doubt about it, but many multinationals I worked for have Windows option only for the Laptops and Desktops.
During years I had to deal with sending files to Linux or Unix (HP UX, Sun Solaris…) to process them and getting back the result. Some sort of ETL and Map Reduce in the prehistory of personal computers, taking in count aspects like Networks speeds too, available space, splitting files for processing.
When I was working as Senior Project Manager in Winterthur Insurance, now Axa, I had to run a lot of ETL (Extract Transform Load) for considerably big files, or when I was project manager and later head of department in Volkswagen gedas or later helping Start ups like Privalia. I can tell you that Windows didn’t like you to open editors to work with 1GB text or CSV file, and doesn’t like it, even if your computer has 16GB of Memory, and even if they do the simplicity of Bash scripts and using pipes, grep, awk… is so powerful that is very convenient to have those files processed using Linux.
And honestly is a pain to send back and forth files to a UNIX System just for Data Crunch. And a VM will be slow and use memory, and you have enable some sort of sharing with it so it can access the Data. Not to talk if you need to split the data files in blocks to be processed in parallel by several computers.
There are many solutions, like using Virtual Machines, Docker, external Servers, etc…
WSL allows you to run Linux command line tools inside Windows.
Having WSL allows things to be done much more straightforward, processing the files in your local windows hard drives.
Please note: Maybe you have enough using GitBash.
Error installing: WslRegisterDistribution failed with error: 0x80070057
When I installed it I found this error and look for an answer online. I found no solutions and many people suffering from the same problem, so I decided to publish an article on how to make it work.
The instructions I detail are based on the documentation from Canonical https://wiki.ubuntu.com/WSL and from Microsoft https://docs.microsoft.com/en-us/windows/wsl/install-win10 and the final solution I found.
Microsoft use Powershell to activate the features disabled in Windows, I did the same with Command Line, which I found more convenient for most of the non extremely tech people.
You will need:
- For x64 systems: Version 1903 or higher, with Build 18362 or higher.
You can check your version of windows opening a Terminal (CMD.exe) and typing:
- For ARM64 systems: Version 2004 or higher, with Build 19041 or higher.
I’m not covering installing WSL for ARM, only for Intel/AMD Desktop/Laptops with Windows 10.
If you’re unsure, you can open a Terminal (CMD.exe) and run:
systeminfo | find "System Type"
If is a x64 system it will return: x64-based PC
Launch CMD.exe as Administrator and type:
dism /online /enable-feature /featurename:Microsoft-Windows-Subsystem-Linux /all /norestart
Enable Virtual Machine Feature:
dism /online /enable-feature /featurename:VirtualMachinePlatform /all /norestart
At this point you have to Restart Windows to complete this part of the installation, otherwise next step won’t work.
Download the Linux Kernel Update Package from here:
Execute wsl_update_x64.msi and grant permissions for modifying the system.
Now it’s crucial that you reboot again. Even if you’re not asked for.
That’s the tricky part.
Then set the version 2 of WSL as default:
C:\WINDOWS\system32>wsl --set-default-version 2 For information on key differences with WSL 2 please visit https://aka.ms/wsl2
Installing Ubuntu (or Kali, or Debian, or openSUSE…)
Open the Microsoft Store or use Microsoft Store link to go directly to the installation of Ubuntu.
You have also several options as indicated in https://wiki.ubuntu.com/WSL:
The recommended way to install Ubuntu on WSL is through the Microsoft Store.
The following Ubuntu releases are available as apps on the Microsoft Store:
- Ubuntu 16.04 LTS (Xenial) is the first release available for WSL. It supports the x64 architecture only. (offline installer: x64)
- Ubuntu 18.04 LTS (Bionic) is the second LTS release and the first one supporting ARM64 systems, too. (offline installers: x64, ARM64)
- Ubuntu 20.04 LTS (Focal) is the current LTS release, supporting both x64 and ARM64 architecture.
- Ubuntu (without the release version) always follows the recommended release, switching over to the next one when it gets the first point release. Right now it installs Ubuntu 20.04 LTS.
Each app creates a separate root file system in which Ubuntu shells are opened but app updates don’t change the root file system afterwards. Installing a different app in parallel creates a different root file system allowing you to have both Ubuntu LTS releases installed and running in case you need it for keeping compatibility with other external systems. You can also upgrade your Ubuntu 16.04 to 18.04 by running ‘do-release-upgrade’ and have three different systems running in parallel, separating production and sandboxes for experiments.
But if you prefer, instead of using the Windows Store, you can download the appx.
In the same page mentioned you can do it for several versions, I attach the link for Ubuntu 20.04 LTS: https://aka.ms/wslubuntu2004
Assuming you used the Windows Store, if you did not reboot and try now to execute it for the first time, or you go to the Command Line and write bash, or open Ubuntu from Windows menu, whatever method you use, you’ll get the abovementioned error.
If that happens to you, just reboot and when you open it will work and will start the install and ask for a user and password:
From here you’re able to update the system, execute the text commands available in Linux, access to the Windows drives, launch htop, git, Python3, apt, wget… copy and paste between windows and Linux terminal, share PATH…
And of course you can run CTOP.py
Take in count that the space reported in / partition is not real, and that you have a 4GB swap.
You can access your C:\ Windows files from:
Happy New Year to all.
- Past year I published some Java Validation Classes for Keyboard input.
Is something very simple, but will help my student friends to validate Input from Keyboard without losing too many hours.
The Input Validation Classes I create in PHP for Privalia or in my PHP Catalonia Framework, are much, much, more powerful, allowing the validation of complete forms, rendering errors, etc… although they were created for Web, and not for Keyboard input.
- I also published a Bash script to count the lines of your programs.
It recursively goes to all the subdirectories looking for .py files, and then it counts the lines.
- I updated the price of my books to be the minimum allowed by LeanPub, to $5 USD, and created a bundle of two of them for $7 USD.
So people can benefit from this during the lock down.
- I’ve updated the Python Combat Guide book with a sample of using Paramiko Libraries for SSH, and increased the Object Oriented Programing and Unit Testing, sections. I also added some books to the Bibliography.
- I’ve read the postmortem initial analysis from Slack’s incident. It’s really interesting.
I cannot share it, but I guess that at some point they will publish it on their blog:
- I’ve been working on an article on How to install the Linux Kernel in Windows 10, with WSL as I got WslRegisterDistribution failed with error: 0x80070057.
Update: The article has been published.
- As I’m giving more Python Classes I decided to write a book to teach to code in Python for non-programmers.