How to change timezone in Linux server (RedHat, CentOS, Ubuntu)

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Learn how to change timezone in the Linux server. Understand timezone files location, configuration files, and way to change timezone using them.

Timezone configuration

This article is a beginner’s guide to change the timezone of the Linux server. Timezone is crucial for the server since the server’s native time is displayed according to timezone.

Server’s current timezone can be checked using simple date command

root@kerneltalks # date
Tue Nov  7 17:23:54 UTC 2017

In the above output, UTC (Coordinated Universal Time) is your server’s timezone. If you want to change it to match your region or application’s user’s timezone there are three ways you can do it.

If you want to change the timezone without much hassle and without messing around system files directly jump to datetimectl command option below.

How to change timezone in Linux using /etc/localtime file

/etc/localtime is the file used by the kernel to determine the timezone. If you check your current file, its a soft link to respective timezone file in /usr/share/zoneinfo directory.

root@kerneltalks # ll /etc/localtime
lrwxrwxrwx. 1 root root 25 Jul 11 16:06 /etc/localtime -> ../usr/share/zoneinfo/UTC

root@kerneltalks # ls -lrt /usr/share/zoneinfo/
total 284
-rw-r--r--.  1 root root 17722 Dec  5  2016 zone1970.tab
-rw-r--r--.  1 root root 19153 Feb 10  2017 zone.tab
-rw-r--r--.  1 root root  4445 Feb 28  2017 iso3166.tab
-rw-r--r--.  6 root root   118 Mar 21  2017 Zulu
-rw-r--r--.  2 root root  1518 Mar 21  2017 W-SU
-rw-r--r--.  1 root root  1873 Mar 21  2017 WET
-rw-r--r--.  6 root root   118 Mar 21  2017 UTC
-rw-r--r--.  6 root root   118 Mar 21  2017 Universal
-rw-r--r--.  2 root root   118 Mar 21  2017 UCT
-rw-r--r--.  3 root root  2126 Mar 21  2017 Turkey
-rw-r--r--.  2 root root   384 Mar 21  2017 Singapore
-rw-r--r--.  2 root root   517 Mar 21  2017 ROK
-rw-r--r--.  2 root root   764 Mar 21  2017 ROC
-rw-r--r--.  1 root root  2294 Mar 21  2017 PST8PDT
-rw-r--r--.  5 root root   388 Mar 21  2017 PRC
-rw-r--r--.  3 root root  3519 Mar 21  2017 posixrules
-rw-r--r--.  2 root root  3439 Mar 21  2017 Portugal
-rw-r--r--.  2 root root  2679 Mar 21  2017 Poland
-rw-r--r--.  2 root root  2047 Mar 21  2017 NZ-CHAT
-rw-r--r--.  4 root root  2434 Mar 21  2017 NZ
-rw-r--r--.  4 root root  2427 Mar 21  2017 Navajo
-rw-r--r--.  1 root root  2294 Mar 21  2017 MST7MDT
-rw-r--r--.  1 root root   118 Mar 21  2017 MST
-rw-r--r--.  1 root root  2102 Mar 21  2017 MET
-rw-r--r--.  2 root root   641 Mar 21  2017 Libya
-rw-r--r--.  2 root root   219 Mar 21  2017 Kwajalein
-rw-r--r--.  2 root root   292 Mar 21  2017 Japan
-rw-r--r--.  2 root root   481 Mar 21  2017 Jamaica
-rw-r--r--.  3 root root  8981 Mar 21  2017 Israel
-rw-r--r--.  2 root root  1690 Mar 21  2017 Iran
-rw-r--r--.  2 root root  1174 Mar 21  2017 Iceland
-rw-r--r--.  1 root root   119 Mar 21  2017 HST
-rw-r--r--.  2 root root  1175 Mar 21  2017 Hongkong
-rw-r--r--. 10 root root   118 Mar 21  2017 Greenwich
-rw-r--r--. 10 root root   118 Mar 21  2017 GMT+0
-rw-r--r--. 10 root root   118 Mar 21  2017 GMT-0
-rw-r--r--. 10 root root   118 Mar 21  2017 GMT0
-rw-r--r--. 10 root root   118 Mar 21  2017 GMT
-rw-r--r--.  7 root root  3661 Mar 21  2017 GB-Eire
-rw-r--r--.  7 root root  3661 Mar 21  2017 GB
-rw-r--r--.  1 root root  2294 Mar 21  2017 EST5EDT
-rw-r--r--.  1 root root   118 Mar 21  2017 EST
-rw-r--r--.  2 root root  3533 Mar 21  2017 Eire
-rw-r--r--.  2 root root  1946 Mar 21  2017 Egypt
-rw-r--r--.  1 root root  1876 Mar 21  2017 EET
-rw-r--r--.  2 root root  2411 Mar 21  2017 Cuba
-rw-r--r--.  1 root root  2294 Mar 21  2017 CST6CDT
-rw-r--r--.  1 root root  2102 Mar 21  2017 CET
drwxr-xr-x.  2 root root   176 Jul 11 15:57 Indian
drwxr-xr-x.  2 root root  4096 Jul 11 15:57 Africa
drwxr-xr-x.  2 root root    53 Jul 11 15:57 Mexico
drwxr-xr-x.  2 root root    59 Jul 11 15:57 Brazil
drwxr-xr-x.  6 root root  8192 Jul 11 15:57 America
drwxr-xr-x.  2 root root   161 Jul 11 15:57 Canada
drwxr-xr-x.  2 root root   187 Jul 11 15:57 Antarctica
drwxr-xr-x.  2 root root    26 Jul 11 15:57 Arctic
drwxr-xr-x.  2 root root  4096 Jul 11 15:57 Asia
drwxr-xr-x.  2 root root   196 Jul 11 15:57 Atlantic
drwxr-xr-x.  2 root root  4096 Jul 11 15:57 Australia
drwxr-xr-x.  2 root root    45 Jul 11 15:57 Chile
drwxr-xr-x.  2 root root  4096 Jul 11 15:57 Etc
drwxr-xr-x.  2 root root  4096 Jul 11 15:57 Europe
drwxr-xr-x.  2 root root   216 Jul 11 15:57 US
drwxr-xr-x.  2 root root  4096 Jul 11 15:57 Pacific
drwxr-xr-x. 18 root root  4096 Jul 11 15:57 posix
drwxr-xr-x. 18 root root  4096 Jul 11 15:57 right

Since our test server’s timezone is UTC, you can see /etc/localtime is a soft link to /usr/share/zoneinfo/UTC. To change the timezone delete existing /etc/localtime file and create a new one with a link to the desired timezone file.

root@kerneltalks #  rm /etc/localtime
rm: remove symbolic link ‘/etc/localtime’? y

root@kerneltalks # ln -s /usr/share/zoneinfo/US/Eastern /etc/localtime

root@kerneltalks # date
Tue Nov  7 12:32:19 EST 2017

You can see we have changed timezone to EST by linking new localtime file to appropriate zone file under /usr/share/zoneinfo

How to change timezone using shell variable TZ

Another way to change the timezone is to use shell variable TZ. You can do it with single line command as below :

root@kerneltalks # export TZ=Asia/Singapore

root@kerneltalks # date
Wed Nov  8 01:36:15 +08 2017

I exported the timezone variable TZ for Singapore timezone. Check the date command output. Timezone has been set to +08 which means UTC+08:00 i.e. SGT (Singapore Timezone)

But remember, this timezone setting will be available for current shell only from where you are exporting this TZ variable.

How to change timezone using /etc/timezone file

The third way to change timezone is through the use of /etc/timezone file. This is available in some distro like Ubuntu. The content of the file will be the timezone name you want to set.

root@kerneltalks # cat /etc/timezone
Etc/UTC

root@kerneltalks # date
Tue Nov  7 17:50:50 UTC 2017

You have to export the timezone variable TZ as well along with a change in /etc/timezone file. And then you can see timezone change in effect.

Change timezone using timedatectl command

You can use timedatectl command to safely change timezone when you don’t want to deal with system files and fear of messing them up.

timedatectl command used to display current timezone, list available timezones, and change timezone on the server. We have this dedicated article on timedatectl to learn this command in detail.

To change timezone of server, use timedatectl with set-timezone argument and its value.

root@kerneltalks # timedatectl set-timezone Africa/Malabo
root@kerneltalks # date
Wed Nov 15 16:59:23 WAT 2017

In the output, you can see we have changed the timezone of the server to the WAT timezone.

All you need to know about sosreport tool

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Understand sosreport in detail. Learn how to generate sosreport and how to read sosreport in this article.

sosreport

sosreport is not a new term for RedHat lovers! Its a tool on RedHat Linux which helps you grab system information in a single tarball which can be shared with the vendor for troubleshooting issues.

Whenever you log a case with RedHat for RHEL, the first thing first they ask is for sosreport. In this article, we will see how to generate a sosreport and how to read sosreport.

If sosreport package is not installed on your system you will see below error –

root@kerneltalks # sosreport
-bash: sosreport: command not found

Install sos package using yum. You can follow the installation steps explained here. Below are the installation logs for your reference.

root@kerneltalks # yum install sos
Loaded plugins: amazon-id, rhui-lb, search-disabled-repos
Resolving Dependencies
--> Running transaction check
---> Package sos.noarch 0:3.4-6.el7 will be installed
--> Processing Dependency: bzip2 for package: sos-3.4-6.el7.noarch
--> Running transaction check
---> Package bzip2.x86_64 0:1.0.6-13.el7 will be installed
--> Finished Dependency Resolution

Dependencies Resolved

========================================================================================================================================================================
 Package                        Arch                            Version                                 Repository                                                 Size
========================================================================================================================================================================
Installing:
 sos                            noarch                          3.4-6.el7                               rhui-REGION-rhel-server-releases                          381 k
Installing for dependencies:
 bzip2                          x86_64                          1.0.6-13.el7                            rhui-REGION-rhel-server-releases                           52 k

Transaction Summary
========================================================================================================================================================================
Install  1 Package (+1 Dependent package)

Total download size: 433 k
Installed size: 1.4 M
Is this ok [y/d/N]: y
Downloading packages:
(1/2): sos-3.4-6.el7.noarch.rpm                                                                                                                  | 381 kB  00:00:00
(2/2): bzip2-1.0.6-13.el7.x86_64.rpm                                                                                                             |  52 kB  00:00:00
------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Total                                                                                                                                   610 kB/s | 433 kB  00:00:00
Running transaction check
Running transaction test
Transaction test succeeded
Running transaction
  Installing : bzip2-1.0.6-13.el7.x86_64                                                                                                                            1/2
  Installing : sos-3.4-6.el7.noarch                                                                                                                                 2/2
  Verifying  : sos-3.4-6.el7.noarch                                                                                                                                 1/2
  Verifying  : bzip2-1.0.6-13.el7.x86_64                                                                                                                            2/2

Installed:
  sos.noarch 0:3.4-6.el7

Dependency Installed:
  bzip2.x86_64 0:1.0.6-13.el7

Complete!

How to generate sosreport

To generate a sosreport you just need to run sosreport command. It saves the report in /var/tmp by default so make sure you have enough breathing space in /var mount point.

Output file follows naming conventions as sosreport-name.caseID-yyyymmddhhmmss.tar.xz where –

  1. name is Name you provide or hostname by default
  2. caseID if you provide or blank
  3. Date in yyyymmdd format
  4. Time in hhmmss

Its a tarball with compression. After running the command it will ask you name and case ID and then start executing its modules which collects all system information and save it into a tarball.

root@kerneltalks # sosreport

sosreport (version 3.4)

This command will collect diagnostic and configuration information from
this Red Hat Enterprise Linux system and installed applications.

An archive containing the collected information will be generated in
/var/tmp/sos.iNadXY and may be provided to a Red Hat support
representative.

Any information provided to Red Hat will be treated in accordance with
the published support policies at:

  https://access.redhat.com/support/

The generated archive may contain data considered sensitive and its
content should be reviewed by the originating organization before being
passed to any third party.

No changes will be made to system configuration.

Press ENTER to continue, or CTRL-C to quit.

Please enter your first initial and last name [kerneltalks]: Shrikant Lavhate
Please enter the case id that you are generating this report for []: 12345678

 Setting up archive ...
 Setting up plugins ...
 Running plugins. Please wait ...

  Running 74/74: yum...            er...
Creating compressed archive...

Your sosreport has been generated and saved in:
  /var/tmp/sosreport-ShrikantLavhate.12345678-20171105171210.tar.xz

The checksum is: 502b698f6052964ca1c2d348ea7e67a4

Please send this file to your support representative.

Command also shows you checksum of the output file. This will be helpful in checking the integrity of the file when it reaches destination party like vendor etc.

root@kerneltalks # ll /var/tmp/sosreport-ShrikantLavhate.12345678-20171105171210.tar.xz
-rw-------. 1 root root 8519732 Nov  5 17:12 /var/tmp/sosreport-ShrikantLavhate.12345678-20171105171210.tar.xz

How to read sosreport

The output report generated above is the tarball file. You can un-tar it and read it on your own as well.

root@kerneltalks # tar xvf /var/tmp/sosreport-ShrikantLavhate.12345678-20171105171210.tar.xz

After extracting tarball you can see directory created with tarball name. Under which you can file many files and directories.

root@kerneltalks # ls -lrt sosreport-ShrikantLavhate.12345678-20171105171210
total 16
drwxr-xr-x.  5 root root   42 Jul 11 15:57 usr
dr-xr-xr-x.  3 root root   19 Jul 11 16:07 boot
dr-xr-xr-x. 10 root root 4096 Nov  5 12:19 proc
dr-xr-xr-x. 10 root root  112 Nov  5 12:19 sys
drwxr-xr-x.  4 root root   28 Nov  5 12:19 var
drwxr-xr-x.  2 root root   18 Nov  5 12:19 dev
dr-xr-xr-x.  7 root root   78 Nov  5 12:24 lib
dr-xr-x---.  2 root root   29 Nov  5 16:23 root
drwxr-xr-x. 34 root root 4096 Nov  5 17:08 etc
lrwxrwxrwx.  1 root root   29 Nov  5 17:12 mount -> sos_commands/filesys/mount_-l
lrwxrwxrwx.  1 root root   27 Nov  5 17:12 df -> sos_commands/filesys/df_-al
lrwxrwxrwx.  1 root root   27 Nov  5 17:12 uptime -> sos_commands/general/uptime
lrwxrwxrwx.  1 root root   28 Nov  5 17:12 uname -> sos_commands/kernel/uname_-a
drwx------.  3 root root   18 Nov  5 17:12 sos_strings
lrwxrwxrwx.  1 root root   25 Nov  5 17:12 lsmod -> sos_commands/kernel/lsmod
lrwxrwxrwx.  1 root root   45 Nov  5 17:12 java -> sos_commands/java/alternatives_--display_java
lrwxrwxrwx.  1 root root   29 Nov  5 17:12 hostname -> sos_commands/general/hostname
lrwxrwxrwx.  1 root root   31 Nov  5 17:12 dmidecode -> sos_commands/hardware/dmidecode
lrwxrwxrwx.  1 root root   25 Nov  5 17:12 date -> sos_commands/general/date
lrwxrwxrwx.  1 root root   32 Nov  5 17:12 route -> sos_commands/networking/route_-n
lrwxrwxrwx.  1 root root   30 Nov  5 17:12 ps -> sos_commands/process/ps_auxwww
lrwxrwxrwx.  1 root root   41 Nov  5 17:12 netstat -> sos_commands/networking/netstat_-W_-neopa
lrwxrwxrwx.  1 root root   22 Nov  5 17:12 last -> sos_commands/last/last
lrwxrwxrwx.  1 root root   34 Nov  5 17:12 ip_addr -> sos_commands/networking/ip_-o_addr
lrwxrwxrwx.  1 root root   24 Nov  5 17:12 free -> sos_commands/memory/free
lrwxrwxrwx.  1 root root  130 Nov  5 17:12 installed-rpms -> sos_commands/rpm/sh_-c_rpm_--nodigest_-qa_--qf_NAME_-_VERSION_-_RELEASE_._ARCH_INSTALLTIME_date_awk_-F_printf_-59s_s_n_1_2_sort_-f
lrwxrwxrwx.  1 root root   38 Nov  5 17:12 chkconfig -> sos_commands/services/chkconfig_--list
-rw-r--r--.  1 root root 1481 Nov  5 17:12 version.txt
drwx------.  2 root root   37 Nov  5 17:12 sos_reports
drwx------.  2 root root   35 Nov  5 17:12 sos_logs
drwx------. 43 root root 4096 Nov  5 17:12 sos_commands
drwxr-xr-x.  3 root root   19 Nov  5 17:12 run

Navigate to sos_reports directory within which you will find sos.txt & sos.html file.

In sos.txt file you can see all the plugins loaded, the command executed, files copied by sosreport. In sos.html file, all these things are hyperlinked to their original content within the directory. So you can directly view command output or files which are copied by script.

If there are any alerts detected by sosreport it will highlight those at the very beginning of these files.

This information is for sosreport version 3.4. If you are running different version there might be small differences in information.

Access denied error in NFS for root account

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Learn how to resolve access denied issues in the NFS mount point. Understand how to root access is limited in NFS and no_root_squash to be used.

Access Denied in NFS for root account

Current setup

Access denied error in NFS share mount points when attempted to create file or directory even if rw option is set while exporting.

I had a directory named mydata which is exported from the NFS server. My /etc/exports file looks like this –

root@kerneltalks # cat /etc/exports
/mydata     10.0.2.34(rw,sync)

I mounted it on the NFS client client1 successfully. I am able to read all data within this directory from the NFS client.

root@client1 # mount kerneltalks:/mydata /nfs_data
root@client1 # ls -lrt /nfs_data

Issue

I am not able to create a file or directory in the NFS mount even if rw option is set. I tried creating files, directory and I get access denied error.

root@client1 # cd /nfs_data

root@client1 # touch testfile
touch: cannot touch ‘testfile’: Access denied

root@client1 # mkdir testdir
mkdir: cannot create directory ‘testdir’: Access denied

Solution

By default, NFS prevents remote root users from gaining root-level privileges on its exports. It assigns user privileges of nfsnobody user  to remotely logged in root users. This is what happened here and hence even if rw option is set, since we are using mount at root user we are not able to write any data on export.

This is called squashing root privileges to the normal ones. This to ensure accidental writing or modifying data on exports. You can set all_squash option which will squash privileges of all remote users including root to normal user nfsnobody.

For our issue, we have to set no_root_squash option on export so that remote root user keeps his power intact and will be able to write on the exported directory.

I changed my /etc/exports as below :

root@kerneltalks # cat /etc/exports
/mydata     10.0.2.34(rw,sync,no_root_squash)

I re-exported directory using exportfs. Re-exporting mount points does not require the client to un-mount exported directories. Re-export also avoid the NFS server restart and catch up with new configuration.

root@kerneltalks # exportfs -ra

That’s it! Now I am able to create files and directories in the exported directory on NFS client.

root@client1 # cd /nfs_data
root@client1 # touch testfile
root@client1 # mkdir testdir

Conclusion

When you are using NFS mount points with root account on client-side then export them with no_root_squash option. This will ensure you don’t face access related issues on NFS mount points.

Googler : Search google right from your Linux terminal

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Learn the search power tool Googler to search keywords on Google from the Linux terminal. The text-based search tool works on all Linux distros.

Googler! Logo @github.com/jarun/googler

One of the most visited sites by IT people is Google! Sample code, syntax, errors, solutions, tutorials, howtos we search all these things on Google every day. No one knows everything! No one can deny that he/she never used Google! So it’s an inseparable part of digital life.

What if you could Google right from your Linux terminal! Sounds crazy! Obviously Googling in text mode won’t be that easy-to-use experience but yes for Linux lovers its fascinating and must-do experience.

In this article, we will walk you through how to Google in Linux terminal.

Googler is a tool that provides the capability to search on Google from the Linux terminal. We will see how to install Googler and how to use Googler to search from the Linux terminal.

About Googler

Googler is a command-line utility originally started by Henri Hakkinen and now taken forward by Arun Jana. Its GIT repo is maintained here. When searched, it shows results with title, link, and excerpt in terminal window.

Take a look of Googler in action :

Googler searching kerneltalks on Google

How to install Googler

The Googler uses Python and the latest release needs Python 3 or later to run. Install Python 3 on your system if you don’t have it.

Now download ready packages for deployment according to your package manager. Get your packages from here: Package managers or OS releases
Install Googler package and you are ready to go.

After a successful package installation, you will be able to run googler command. If you want to compile it on your system using source code then source code is available here.

How to use Googler

Googler has many options to search and interact with results. For simple search you just supply keyword and it will show you the first 10 search results the same as Google website do when you search keyword from browser.

Output is color coded for easy reading and identification where –

  • Green for titles
  • Yellow for links
  • cyan for indices and link metadata like published date etc.
  • Normal for link description

See above screenshot where you can see simple keyword search in googler and the color scheme.

If you run googler command without any argument it asks for a keyword or offers help via ?

root@kerneltalks # googler
Please initiate a query.
googler (? for help) ?

omniprompt keys:
  n, p                  fetch the next or previous set of search results
  index                 open the result corresponding to index in browser
  f                     jump to the first page
  o [index|range|a ...] open space-separated result indices, numeric ranges
                        (sitelinks unsupported in ranges), or all, in browser
                        open the current search in browser, if no arguments
  O [index|range|a ...] like key 'o', but try to open in a GUI browser
  g keywords            new Google search for 'keywords' with original options
                        should be used to search omniprompt keys and indices
  q, ^D, double Enter   exit googler
  ?                     show omniprompt help
  *                     other inputs issue a new search with original options

Here are few searches you can try with Googler :

Search within news for keyword

# googler -N Linux

Search on specific website

# googler -w kerneltalks.com nfs

Search specific filetype

# googler linux tutorial filetype:pdf

Many options to explore and use. Check googler manpage using man googler or help using googler -h !!

Enjoy! Happy Googling from Terminal!

Install Python 3 on Linux (Redhat, CentOS, Ubuntu)

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Learn how to install python 3 on Linux like Redhat, centos, ubuntu, etc. Also, learn how to get rid of a few python related errors. 

Python 3 installation steps

By default, all of the Linux distros have pre-installed Python. Most of it is Python 2.x. not Python 3.x. Many of nowadays tools, scripts, etc need Python version 3 (python3) for compiling.

In this article, we will see how to install python3 step by step on Linux like RHEL, centos, ubuntu, etc.

If your package manager repo does offer python3 for install then you can easily install it from there,. If not then follow this process to install from source code.

Let’s get into the step by step Python installation from its source code. As of today, the Latest Python release is 3.6.3 and it’s available here.

Step 1.

Download source code from the Python website on your server using tools like wget. We are using the latest release link here.

root@kerneltalks # wget https://www.python.org/ftp/python/3.6.3/Python-3.6.3.tar.xz
--2017-11-05 12:13:48--  https://www.python.org/ftp/python/3.6.3/Python-3.6.3.tar.xz
Resolving www.python.org (www.python.org)... 151.101.8.223, 2a04:4e42:2::223
Connecting to www.python.org (www.python.org)|151.101.8.223|:443... connected.
HTTP request sent, awaiting response... 200 OK
Length: 16974296 (16M) [application/octet-stream]
Saving to: ‘Python-3.6.3.tar.xz’

100%[==============================================================================================================================>] 16,974,296  4.21MB/s   in 4.0s

2017-11-05 12:13:52 (4.01 MB/s) - ‘Python-3.6.3.tar.xz’ saved [16974296/16974296]

Step 2.

Un-tar downloaded file and navigate to newly created Python directory Python-3.6.3. Also, make sure you have a GCC package installed on your system. If not install package gcc before proceeding to the next step.

root@kerneltalks # tar xf Python-3.6.3.tar.xz
root@kerneltalks # cd Python-3.6.3

Step 3.

Now its time to compile the source code. Execute configure script in Python-3.6.3 directory.

root@kerneltalks # ./configure
checking build system type... x86_64-pc-linux-gnu
checking host system type... x86_64-pc-linux-gnu
checking for python3.6... no
checking for python3... no
checking for python... python
checking for --enable-universalsdk... no
checking for --with-universal-archs... no
checking MACHDEP... linux
checking for --without-gcc... no
checking for --with-icc... no
checking for gcc... gcc
checking whether the C compiler works... yes
checking for C compiler default output file name... a.out
checking for suffix of executables...
checking whether we are cross compiling... no
checking for suffix of object files... o
checking whether we are using the GNU C compiler... yes
checking whether gcc accepts -g... yes
checking for gcc option to accept ISO C89... none needed
checking how to run the C preprocessor... gcc -E
checking for grep that handles long lines and -e... /bin/grep
checking for a sed that does not truncate output... /bin/sed
checking for --with-cxx-main=<compiler>... no
checking for g++... no
configure:

  By default, distutils will build C++ extension modules with "g++".
  If this is not intended, then set CXX on the configure command line.

checking for the platform triplet based on compiler characteristics... x86_64-linux-gnu
checking for -Wl,--no-as-needed... yes
checking for egrep... /bin/grep -E
checking for ANSI C header files... yes
checking for sys/types.h... yes
checking for sys/stat.h... yes
checking for stdlib.h... yes
checking for string.h... yes
checking for memory.h... yes
checking for strings.h... yes
checking for inttypes.h... yes
checking for stdint.h... yes
checking for unistd.h... yes
checking minix/config.h usability... no
checking minix/config.h presence... no
checking for minix/config.h... no
checking whether it is safe to define __EXTENSIONS__... yes
checking for the Android API level... not Android
checking for --with-suffix...
checking for case-insensitive build directory... no
checking LIBRARY... libpython$(VERSION)$(ABIFLAGS).a
checking LINKCC... $(PURIFY) $(MAINCC)
checking for GNU ld... yes
checking for inline... inline
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configure: creating ./config.status
config.status: creating Makefile.pre
config.status: creating Modules/Setup.config
config.status: creating Misc/python.pc
config.status: creating Misc/python-config.sh
config.status: creating Modules/ld_so_aix
config.status: creating pyconfig.h
creating Modules/Setup
creating Modules/Setup.local
creating Makefile


If you want a release build with all stable optimizations active (PGO, etc),
please run ./configure --enable-optimizations

Step 4.

Now run make followed by make install to complete the installation. Both commands output is not given here since its pretty long.

root@kerneltalks # make
root@kerneltalks # make install

Step 5.

Check Python installed version from Python prompt.

root@kerneltalks # python3
Python 3.6.3 (default, Nov  5 2017, 12:28:06)
[GCC 4.8.5 20150623 (Red Hat 4.8.5-16)] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>>

You can see in the above output Python 3.6.3 shows we have installed python v3 successfully.

Troubleshooting Python issues

When using or compiling Python programs you might run into below errors. I have listed their solutions for your quick reference.

Error :  ImportError: No module named 'zlib'

Solution: Install zlib-devel (zlib development tools) package and re-install python

Error : ImportError: cannot import name 'HTTPSConnection'

Solution: Install OpenSSL-devel  (Open SSL development tools) package and re-install python

Error : zipimport.ZipImportError: can't decompress data; zlib not available

Solution: This error is seen during Python installation if zlib is not installed on the server. Install zlib package

What are the huge pages in Linux?

9 Replies

Learn about huge pages in Linux. Understand what is huge pages, how to configure it, how to check the current state, and how to disable it.

HugePages in Linux

In this article, we will walk you through details about huge pages so that you will be able to answer: what are huge pages in Linux? How to enable/disable huge pages? How to determine huge page value? in Linux like RHEL6, RHEL7, Ubuntu, etc.

Lets start with Huge pages basics.

What is Huge page in Linux?

Huge pages are helpful in virtual memory management in the Linux system. As the name suggests, they help is managing huge size pages in memory in addition to standard 4KB page size. You can define as huge as 1GB page size using huge pages.

During system boot, you reserve your memory portion with huge pages for your application. This memory portion i.e. these memory occupied by huge pages is never swapped out of memory. It will stick there until you change your configuration. This increases application performance to a great extent like Oracle database with pretty large memory requirements.

Why use huge page?

In virtual memory management, the kernel maintains a table in which it has a mapping of the virtual memory address to a physical address. For every page transaction, the kernel needs to load related mapping. If you have small size pages then you need to load more numbers of pages resulting kernel to load more mapping tables. This decreases performance.

Using huge pages means you will need fewer pages. This decreases the number of mapping tables to load by the kernel to a great extent. This increases your kernel-level performance which ultimately benefits your application.

In short, by enabling huge pages, the system has fewer page tables to deal with and hence less overhead to access/maintain them!

How to configure huge pages?

Run below command to check current huge pages details.

root@kerneltalks # grep Huge /proc/meminfo
AnonHugePages:         0 kB
HugePages_Total:       0
HugePages_Free:        0
HugePages_Rsvd:        0
HugePages_Surp:        0
Hugepagesize:       2048 kB

In the above output, you can see the one-page size is 2MB Hugepagesize and a total of 0 pages on the system HugePages_Total. This huge page size can be increased from 2MB to max 1GB.

Run below script to get how much huge pages your system needs currently. The script is from Oracle and can be found.

#!/bin/bash
#
# hugepages_settings.sh
#
# Linux bash script to compute values for the
# recommended HugePages/HugeTLB configuration
#
# Note: This script does calculation for all shared memory
# segments available when the script is run, no matter it
# is an Oracle RDBMS shared memory segment or not.
# Check for the kernel version
KERN=`uname -r | awk -F. '{ printf("%d.%d\n",$1,$2); }'`
# Find out the HugePage size
HPG_SZ=`grep Hugepagesize /proc/meminfo | awk {'print $2'}`
# Start from 1 pages to be on the safe side and guarantee 1 free HugePage
NUM_PG=1
# Cumulative number of pages required to handle the running shared memory segments
for SEG_BYTES in `ipcs -m | awk {'print $5'} | grep "[0-9][0-9]*"`
do
   MIN_PG=`echo "$SEG_BYTES/($HPG_SZ*1024)" | bc -q`
   if [ $MIN_PG -gt 0 ]; then
      NUM_PG=`echo "$NUM_PG+$MIN_PG+1" | bc -q`
   fi
done
# Finish with results
case $KERN in
   '2.4') HUGETLB_POOL=`echo "$NUM_PG*$HPG_SZ/1024" | bc -q`;
          echo "Recommended setting: vm.hugetlb_pool = $HUGETLB_POOL" ;;
   '2.6' | '3.8' | '3.10' | '4.1' ) echo "Recommended setting: vm.nr_hugepages = $NUM_PG" ;;
    *) echo "Unrecognized kernel version $KERN. Exiting." ;;
esac
# End

You can save it in /tmp as hugepages_settings.sh and then run it like below :

root@kerneltalks # sh /tmp/hugepages_settings.sh
Recommended setting: vm.nr_hugepages = 124

Output will be similar to some number as shown in above sample output.

This means your system needs 124 huge pages of 2MB each! If you have set 4MB as page size then the output would have been 62. You got the point, right?

Configure hugepages in kernel

Now last part is to configure the above-stated kernel parameter and reload it. Add below value in /etc/sysctl.conf and reload configuration by issuing sysctl -p command.

vm.nr_hugepages=126

Notice that we added 2 extra pages in the kernel since we want to keep a couple of pages spare than the actual required number.

Now, huge pages have been configured in the kernel but to allow your application to use them you need to increase memory limits as well. The new memory limit should be 126 pages x 2 MB each = 252 MB i.e. 258048 KB.

You need to edit below settings in /etc/security/limits.conf

soft memlock 258048 
hard memlock 258048

Sometimes these settings are configured in app-specific files like for Oracle DB its in  /etc/security/limits.d/99-grid-oracle-limits.conf

That’s it! You might want to restart your application to make use of these new huge pages.

How to disable hugepages?

HugePages are generally enabled by default. Use the below command to check the current state of huge pages.

root@kerneltalks # cat /sys/kernel/mm/transparent_hugepage/enabled
[always] madvise never

[always] flag in output shows that hugepages are enabled on system.

For RedHat based systems file path is /sys/kernel/mm/redhat_transparent_hugepage/enabled

If you want to disable huge pages then add transparent_hugepage=never at the end of kernel line in /etc/grub.conf and reboot the system.

check_mk error Cannot fetch deployment URL via curl error

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Article explaining ‘ERROR Cannot fetch deployment URL via curl: Couldn’t resolve host. The given remote host was not resolved.’ and how to resolve it.

check_mk register error

check_mk is a utility that helps you configure your server to be monitored via nagios monitoring tool. While configuring one of the clients I came across below error :

ERROR Cannot fetch deployment URL via curl: Couldn't resolve host. The given remote host was not resolved.

This error came after I tried to register the client with the monitoring server with below command :

root@kerneltalks # /usr/bin/cmk-update-agent register -s monitor.kerneltalks.com -i master -H `hostname` -p http -U omdadmin -S ASFKWEFUNSHEFKG -v

Here in this command –

-s is monitoring server
-i is Name of Check_MK site on that server
-H is Hostname to fetch agent for
-p is protocol Either HTTP or HTTPS (default is HTTPS)
-U  User-ID of a user who is allowed to download the agent.
-S is secret. Automation secret of that user (in case of automation user)
From the error, you can figure out that command is not able to resolve to monitor server DNS name monitor.kerneltalks.com

Solution

Its pretty simple. Check /etc/resolv.conf to make sure that you have proper DNS server entry for your environment. If it still doesn’t resolve the issue then you can add an entry in /etc/hosts for it.

root@kerneltalks # cat /etc/hosts
10.0.10.9 monitor.kerneltalks.com

Thats it. You would be able to register now successfully.

root@kerneltalks # /usr/bin/cmk-update-agent register -s monitor.kerneltalks.com -i master -H `hostname` -p http -U omdadmin -S ASFKWEFUNSHEFKG -v
Going to register agent at deployment server
Successfully registered agent for deployment.
You can now update your agent by running 'cmk-update-agent -v'
Saved your registration settings to /etc/cmk-update-agent.state.

By the way, you can directly use the IP address for -s switch and get rid of all the above jargon including error itself!

mount.nfs: requested NFS version or transport protocol is not supported

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Troubleshooting error ‘mount.nfs: requested NFS version or transport protocol is not supported’ and how to resolve it. 

Resolve NFS error

Another troubleshooting article aimed at specific errors and help you how to solve it. In this article, we will see how to resolve error ‘mount.nfs: requested NFS version or transport protocol is not supported’ seen on NFS client while trying to mount NFS share.

# mount 10.0.10.20:/data /data_on_nfs
mount.nfs: requested NFS version or transport protocol is not supported

Sometimes you see error mount.nfs: requested NFS version or transport protocol is not supported when you try to mount NFS share on NFS client. There are couple of reasons you see this error :

  1. NFS services are not running on NFS server
  2. NFS utils not installed on the client
  3. NFS service hung on NFS server

NFS services at the NFS server can be down or hung due to multiple reasons like server utilization, server reboot, etc.

You might be interested in reading :

Solution 1:

To get rid of this error and successfully mount your share follow the below steps.

Login to the NFS server and check the NFS services status.

[root@kerneltalks]# service nfs status
rpc.svcgssd is stopped
rpc.mountd is stopped
nfsd is stopped
rpc.rquotad is stopped

In the above output you can see the NFS services are stopped on the server. Start them.

[root@kerneltalks]# service nfs start
Starting NFS services: [ OK ]
Starting NFS quotas: [ OK ]
Starting NFS mountd: [ OK ]
Starting NFS daemon: [ OK ]
Starting RPC idmapd: [ OK ]

You might want to check for nfs-server or nfsserver service as well depends on your Linux distro.

Now try to mount NFS share on the client. And you will be able to mount them using the same command we see earlier!

Solution 2 :

If that doesn’t work for you then try installing package nfs-utils on your server and you will get through this error.

Solution 3 :

Open file /etc/sysconfig/nfs and try to check below parameters

# Turn off v4 protocol support
#RPCNFSDARGS="-N 4"
# Turn off v2 and v3 protocol support
#RPCNFSDARGS="-N 2 -N 3"

Removing hash from RPCNFSDARGS lines will turn off specific version support. This way clients with mentioned NFS versions won’t be able to connect to the NFS server for mounting share. If you have any of it enabled, try disabling it and mounting at the client after the NFS server service restarts.

Let us know if you have faced this error and solved it by any other methods in the comments below. We will update our article with your information to keep it updated and help the community live better!

How to test internet speed in Linux terminal

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Learn how to use speedtest CLI tool to test internet speed in the Linux terminal. It also includes a one-liner python command to get speed details right away.

Internet speed check in Linux

Most of us check the internet bandwidth speed whenever we connect to a new network or wifi. So why not our servers! Here is a tutorial that will walk you through to test internet speed in the Linux terminal.

Every one of us generally uses Speedtest by Ookla to check internet speed. It’s a pretty simple process for a desktop. Go to their website and just click the GO button. It will scan your location and speed test with the nearest server.  If you are on mobile, they have their app for you. But if you are on the terminal with command-line interface things are little different. Let’s see how to check internet speed from the Linux terminal.

If you want to speed check only once and don’t want to download the tool on the server, jump here and see one-liner command.

Step 1 : Download speedtest cli tool

First of all, you have to download speedtest CLI tool from the GitHub repository. Nowadays, it also included in many well known Linux repositories as well. If it’s there then you can directly install that package on your Linux distro.

Let’s proceed with the Github download and install process. Install the git package depending on your distro. Then clone Github repo of speedtest like below:

[root@kerneltalks ~]# git clone https://github.com/sivel/speedtest-cli.git
Cloning into 'speedtest-cli'...
remote: Counting objects: 913, done.
remote: Total 913 (delta 0), reused 0 (delta 0), pack-reused 913
Receiving objects: 100% (913/913), 251.31 KiB | 143.00 KiB/s, done.
Resolving deltas: 100% (518/518), done.

It will be cloned to your present working directory. A new directory named speedtest-cli will be created. You can see the below files in it.

[root@kerneltalks ~]# cd speedtest-cli
[root@kerneltalks speedtest-cli]# ll
total 96
-rw-r--r--. 1 root root  1671 Oct  7 16:55 CONTRIBUTING.md
-rw-r--r--. 1 root root 11358 Oct  7 16:55 LICENSE
-rw-r--r--. 1 root root    35 Oct  7 16:55 MANIFEST.in
-rw-r--r--. 1 root root  5215 Oct  7 16:55 README.rst
-rw-r--r--. 1 root root    20 Oct  7 16:55 setup.cfg
-rw-r--r--. 1 root root  3196 Oct  7 16:55 setup.py
-rw-r--r--. 1 root root  2385 Oct  7 16:55 speedtest-cli.1
-rw-r--r--. 1 root root  1200 Oct  7 16:55 speedtest_cli.py
-rwxr-xr-x. 1 root root 47228 Oct  7 16:55 speedtest.py
-rw-r--r--. 1 root root   333 Oct  7 16:55 tox.ini

The python script speedtest.py is the one we will be using to check internet speed.

You can link this script for a command in /usr/bin so that all users on the server can use it. Or you can even create command alias for it and it will be easy for all users to use it.

Step 2 : Run python script

Now, run a python script without any argument and it will search the nearest server and test your internet speed.

[root@kerneltalks speedtest-cli]# python speedtest.py
Retrieving speedtest.net configuration...
Testing from Amazon (35.154.184.126)...
Retrieving speedtest.net server list...
Selecting best server based on ping...
Hosted by Spectra (Mumbai) [1.15 km]: 8.174 ms
Testing download speed................................................................................
Download: 548.13 Mbit/s
Testing upload speed................................................................................................
Upload: 323.95 Mbit/s

I am on the AWS EC2 Linux server. That’s the bandwidth of the Amazon data center! 🙂

Different options with script

Few options which might be useful are as below :

To search speedtest servers nearby your location use --list switch and grep for your location name.

[root@kerneltalks speedtest-cli]#  python speedtest.py --list | grep -i mumbai
 2827) Bharti Airtel Ltd (Mumbai, India) [1.15 km]
 8978) Spectra (Mumbai, India) [1.15 km]
 4310) Hathway Cable and Datacom Ltd (Mumbai, India) [1.15 km]
 3315) Joister Broadband (Mumbai, India) [1.15 km]
 1718) Vodafone India (Mumbai, India) [1.15 km]
 6454) YOU Broadband India Pvt Ltd. (Mumbai, India) [1.15 km]
 9764) Railtel Corporation of india Ltd (Mumbai, India) [1.15 km]
 9584) Sheng Li Telecom (Mumbai, India) [1.15 km]
 7605) Idea Cellular Ltd. (Mumbai, India) [1.15 km]
 8122) Sify Technologies Ltd (Mumbai, India) [1.15 km]
 9049) I-ON (Mumbai, India) [1.15 km]
 6403) YOU Broadband India Pvt Ltd., Mumbai (Mumbai, India) [1.15 km]

You can see here, the first column is a server identifier followed by the name of the company hosting that server, location, and finally its distance from your location.

To test the internet speed using specific server use --server switch and server identifier from the previous output as an argument.

[root@kerneltalks speedtest-cli]# python speedtest.py --server 2827
Retrieving speedtest.net configuration...
Testing from Amazon (35.154.184.126)...
Retrieving speedtest.net server list...
Selecting best server based on ping...
Hosted by Bharti Airtel Ltd (Mumbai) [1.15 km]: 13.234 ms
Testing download speed................................................................................
Download: 93.47 Mbit/s
Testing upload speed................................................................................................
Upload: 69.25 Mbit/s

To get the share link of your speed test, use –share switch. It will give you the URL of your test hosted on speedtest website. You can share this URL.

[root@kerneltalks speedtest-cli]# python speedtest.py --share
Retrieving speedtest.net configuration...
Testing from Amazon (35.154.184.126)...
Retrieving speedtest.net server list...
Selecting best server based on ping...
Hosted by Spectra (Mumbai) [1.15 km]: 7.471 ms
Testing download speed................................................................................
Download: 621.00 Mbit/s
Testing upload speed................................................................................................
Upload: 367.37 Mbit/s
Share results: http://www.speedtest.net/result/6687428141.png

Observe the last line which includes the URL of your test result. If I download that image its the one below :

Speedtest result on Linux

That’s it! But hey if you don’t want all this technical jargon, you can even use below one-liner to get speed test done right away.

Internet speed test using one liner in terminal

We are going to use a curl tool to fetch the above python script online and supply it to python for execution on the go!

[root@kerneltalks ~]# curl -s https://raw.githubusercontent.com/sivel/speedtest-cli/master/speedtest.py | python -

Above command will run the script and show you result on screen!

[root@kerneltalks speedtest-cli]# curl -s https://raw.githubusercontent.com/sivel/speedtest-cli/master/speedtest.py | python -
Retrieving speedtest.net configuration...
Testing from Amazon (35.154.184.126)...
Retrieving speedtest.net server list...
Selecting best server based on ping...
Hosted by Spectra (Mumbai) [1.15 km]: 12.599 ms
Testing download speed................................................................................
Download: 670.88 Mbit/s
Testing upload speed................................................................................................
Upload: 355.84 Mbit/s

I tested this tool on RHEL 7 server but the process is same on Ubuntu, Debian, Fedora, or CentOS.