Yearly Archives: 2017

Date & time management in Linux using timedatectl command

Learn timezone management using timedatectl command. An article explaining different uses of timedatectl command along with examples.

In our previous article, we have seen how to change the timezone of the Linux server using files or variables in the system. Few of our readers pushed timedatectl command to achieve this task easily. So I thought of writing a separate article on timedatectl command explaining all its usage.

In this article, we will see how to display server time details, view, list, and change the timezone of the server using timedatectl command. If you want to use date or time in a shell script or as a variable, we explained here how to format the date and time to use it as variable or in scripting.

timedatectl is Time Date Control command! It used to control the date and time of the server in Linux. To check your current system date and time details, run this command without any switch –

root@kerneltalks # timedatectl
      Local time: Wed 2017-11-15 15:58:33 UTC
  Universal time: Wed 2017-11-15 15:58:33 UTC
        RTC time: Wed 2017-11-15 15:58:32
       Time zone: UTC (UTC, +0000)
     NTP enabled: yes
NTP synchronized: yes
 RTC in local TZ: no
      DST active: n/a

Where,

Local time : Your system’s local date and time
Universal time : Current UTC time
RTC time : Current Real-time clock time
Time zone : Your system’s current timezone
NTP enabled : Is NTP is enabled on system or not
NTP synchronized : NTP time synced or not.
RTC in local TZ : Is RTC maintaining in configured system TZ? It is recommended to keep it off.
DST active : Daylight saving time enabled or not

List and change timezone using timedatectl

timedatectl allow you to change the timezone of the system with a list of available timezones. To view, a list of available timezones use the command with list-timezones switch.

root@kerneltalks # timedatectl list-timezones
Africa/Abidjan
Africa/Accra
Africa/Addis_Ababa
Africa/Algiers
Africa/Asmara
Africa/Bamako
----- output clipped-----

You will be presented with a list of available timezones in a paged manner. You can use any of thee timezones to set on your local system. To change timezone of your system use set-timezone switch.

root@kerneltalks # timedatectl set-timezone Australia/Sydney

Above command will change server timezone to Australia/Sydney one.

Change date and time using timedatectl

Most of the servers are configured with NTP these days. But if not and/or if you want to change the date and time manually then you can use set-time switch. Time should be supplied with YYYY-MM-DD HH:MM:SS

root@kerneltalks # timedatectl set-time "2018-01-01 12:12:12"

If NTP is configured then you might see an error Failed to set time: Automatic time synchronization is enabled when attempting to change system time manually.

Enable/Disable RTC and NTP using timedatectl

You can enable or disable RTC (Real Time Clock) and NTP using timedatectl. For RTC use set-local-rtc and for NTP use set-ntp switch. Both arguments accepts 1 (to enable) and 0 (to disable) as values.

root@kerneltalks # timedatectl set-ntp 0
root@kerneltalks # timedatectl set-local-rtc 0

Please note that enabling NTP here does not take you through NTP configuration steps. That has to be done separately. This only controls if the system should sync time using configured NTP or not.

Manage date and time of other machine

You can use timedatectl command to manage the date and time of local containers or remote machines. To manage the time of local container use -M switch whereas to connect to the remote host and manage its time use -H switch.

-M switch takes argument as --host=ip/hostname. -H switch takes argument as --machine=container_name.

That’s all switches which are mainly useful in day-to-day operations. There are a few more that can be referred from its man page.

How to troubleshoot RPC: Port mapper failure – Timed out error

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Learn how to troubleshoot RPC: Port mapper failure – Timed out error on NFS client. This will help you to resolve NFS mounting being timed out issue.

In this article, we are going to discuss the troubleshooting of one of the NFS errors you see on NFS clients. This error can be seen while trying commands related to NFS like below :

root@kerneltalks # showmount -e mynfsserver
clnt_create: RPC: Port mapper failure - Timed out

root@kerneltalks # rpcinfo -p  mynfsserver
mynfsserver: RPC: Port mapper failure - Timed out

Normally when you see this error you are not able to mount NFS share as well. You will see mount.nfs: Connection timed out error when you try to mount NFS share.

root@kerneltalks # mount mynfsserver:/data /nfs_data
mount.nfs: Connection timed out

Troubleshooting steps

Follow below troubleshooting steps to fix RPC: Port mapper failure - Timed out error.

Check NFS services on NFS server

First, check if NFS server services are running smoothly on the NFS server.

root@mynfsserver # service nfs-server status
nfs-server.service - NFS server and services
   Loaded: loaded (/usr/lib/systemd/system/nfs-server.service; disabled)
  Drop-In: /usr/lib/systemd/system/nfs-server.service.d
           └─nfsserver.conf
        /run/systemd/generator/nfs-server.service.d
           └─order-with-mounts.conf
   Active: active (exited) since Tue 2017-11-07 15:58:08 BRST; 6 days ago
 Main PID: 1586 (code=exited, status=0/SUCCESS)
   CGroup: /system.slice/nfs-server.service

The above output is from the Suse Linux server. The output may look different n different Linux distros. If it’s not running or hung, you may need to restart NFS services.

Check connectivity between NFS server and client

Make sure you are able to reach the NFS server from your client. Check using ping and telnet to NFS ports like 111 and 2049 over both protocols TCP and UDP.

root@kerneltalks #  ping mynfsserver
PING lasnfsp01v.la.holcim.net (10.186.1.22) 56(84) bytes of data.
64 bytes from 10.186.1.22: icmp_seq=1 ttl=56 time=3.92 ms
64 bytes from 10.186.1.22: icmp_seq=2 ttl=56 time=3.74 ms
64 bytes from 10.186.1.22: icmp_seq=3 ttl=56 time=3.82 ms
^C
--- mynfsserver ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2003ms
rtt min/avg/max/mdev = 3.748/3.830/3.920/0.086 ms

root@kerneltalks # telnet 10.186.1.22 2049
Trying 10.186.1.22...
Connected to 10.186.1.22.
Escape character is '^]'.

root@kerneltalks # nc -v -u mynfsserver 111
Connection to mynfsserver 111 port [udp/sunrpc] succeeded!
^C
root@kerneltalks # nc -v -u mynfsserver 2049
Connection to mynfsserver 2049 port [udp/nfs] succeeded!
^C
root@kerneltalks # nc -v mynfsserver 111
Connection to mynfsserver 111 port [tcp/sunrpc] succeeded!
^C
root@kerneltalks # nc -v mynfsserver 2049
Connection to mynfsserver 2049 port [tcp/nfs] succeeded!
^C

Check if RPC info is reachable from client

Run below command to check if you can read RPC information of the NFS server from the client machine.

root@kerneltalks # rpcinfo -p 10.186.1.22
   program vers proto   port  service
    100000    4   udp    111  portmapper
    100000    3   udp    111  portmapper
    100000    2   udp    111  portmapper
    100000    4   tcp    111  portmapper
    100000    3   tcp    111  portmapper
    100000    2   tcp    111  portmapper
    100005    1   udp  20048  mountd
    100005    1   tcp  20048  mountd
    100005    2   udp  20048  mountd
    100005    2   tcp  20048  mountd
    100005    3   udp  20048  mountd
    100005    3   tcp  20048  mountd
    100024    1   udp   4000  status
    100024    1   tcp   4000  status
    100003    3   tcp   2049  nfs
    100003    4   tcp   2049  nfs
    100227    3   tcp   2049  nfs_acl
    100003    3   udp   2049  nfs
    100003    4   udp   2049  nfs
    100227    3   udp   2049  nfs_acl
    100021    1   udp   4001  nlockmgr
    100021    3   udp   4001  nlockmgr
    100021    4   udp   4001  nlockmgr
    100021    1   tcp   4001  nlockmgr
    100021    3   tcp   4001  nlockmgr
    100021    4   tcp   4001  nlockmgr

If you have connectivity issue then you will see mynfsserver: RPC: Port mapper failure - Timed out error here.

Check if you can read exported share info from client

Use the below command to check if you can read exported share info from the client.

root@kerneltalks # showmount -e  10.186.1.22
Export list for  10.186.1.22:
/data *(rw,sync,no_root_squash)

Check if antivirus kernel modules are blocking the NFS

Lastly, if you have SEP 14 (Symantec Endpoint Protection) antivirus installed on your server then you need to uninstall it. For some mysterious reason, SEP 14 holds on nfsd and crashes everything to NFS. You may see below messages in dmesg of NFS server to verify if SEP kernel modules are messing up with NFS

symev_custom_4_12_14_95_48_default_x86_64: loading out-of-tree module taints kernel.
symev_custom_4_12_14_95_48_default_x86_64: module verification failed: signature and/or required key missing - tainting kernel
symap_custom_4_12_14_95_48_default_x86_64: module license 'Proprietary' taints kernel.
symev: hold nfsd module
BUG: unable to handle kernel paging request at ffffffffc068f8b4
IP: svc_tcp_accept+0x1a6/0x320 [sunrpc]

You need a reboot after uninstalling antivirus since its kernel modules loaded in kernel won’t get freed with uninstall. For that, you need to reboot the server. You cant even remove it from the kernel as you normally remove the module from the running kernel. So reboot is a way to go after uninstalling antivirus.

root@kerneltalks # lsmod |grep sym
symev_custom_4_12_14_95_48_default_x86_64    98304  1

root@kerneltalks # modprobe -r symev_custom_4_12_14_95_48_default_x86_64
modprobe: FATAL: Module symev_custom_4_12_14_95_48_default_x86_64 is in use.

root@kerneltalks # rmmod  symev_custom_4_12_14_95_48_default_x86_64
rmmod: ERROR: Module symev_custom_4_12_14_95_48_default_x86_64 is in use

root@kerneltalks # lsmod | grep sym
symev_custom_4_12_14_95_48_default_x86_64    98304  1

root@kerneltalks # modinfo symev_custom_4_12_14_95_48_default_x86_64
filename:       /lib/modules/4.12.14-95.48-default/kernel/drivers/char/symev-custom-4-12-14-95-48-default-x86-64.ko
modinfo: ERROR: could not get modinfo from 'symev_custom_4_12_14_95_48_default_x86_64': No such file or directory

Once all the above commands are able to provide you expected output, you will then be ready to mount your share without any issues and the issue will be resolved.

How to resolve connectivity issue

To resolve connectivity between two servers first you need to check on network ends that two servers are able to communicate over a network. If you are running it on AWS Linux EC2 instances then you might need to check security groups to allow proper traffic.

On the OS front, you may need to check iptables settings and allow NFS ports. SELinux is also an area where you need to explore settings if you have customized SELinux running on your server. Normally by default SELinux allows NFS traffic.

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.

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.

How to configure login banners in Linux (RedHat, Ubuntu, CentOS, Fedora)

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Learn how to create login banners in Linux to display a different warning or information message to the user who is about to log in or after he logs in.

Whenever you log in to some production systems of the firm, you get to see some login messages, warnings, or info about the server you are about to log in or already logged in like below. Those are the login banners.

In this article we will walk you through how to configure them.

There are two types of banners you can configure.

Banner message to display before user logs in (configure in the file of your choice eg. /etc/login.warn)
Banner message to display after the user successfully logged in (configure in /etc/motd)

How to display message when user connects to system before login

This message will be displayed to the user when he connects to the server and before he logged in. This means when he enter the username, this message will be displayed before the password prompt.

You can use any filename and enter your message within. Here we used /etc/login.warn file and put our messages inside.

# cat /etc/login.warn
        !!!! Welcome to KernelTalks test server !!!!
This server is meant for testing Linux commands and tools. If you are
not associated with kerneltalks.com and not authorized please dis-connect
immediately.

Now, you need to supply this file and path to sshd daemon so that it can fetch this banner for each user login request. For that open /etc/sshd/sshd_config file and search for the line #Banner none

Here you have to edit the file and write your filename and remove the hash mark. It should look like : Banner /etc/login.warn

Save the file and restart sshd daemon. To avoid disconnecting existing connected users, use the HUP signal to restart sshd.

root@kerneltalks # ps -ef |grep -i sshd
root     14255     1  0 18:42 ?        00:00:00 /usr/sbin/sshd -D
root     19074 14255  0 18:46 ?        00:00:00 sshd: ec2-user [priv]
root     19177 19127  0 18:54 pts/0    00:00:00 grep -i sshd

root@kerneltalks # kill -HUP 14255

That’s it! Open new sessions and try login. You will be greeted with the message you configured in the above steps.

You can see the message is displayed before the user enters his password and log in to the system.

How to display message after user logs in

Message user sees after he logs into the system successfully is Message Of The Day & is controlled by /etc/motd file. Edit this file and enter the message you want to greet the user with once he successfully logged in.

root@kerneltalks # cat /etc/motd
           W E L C O M E
Welcome to the testing environment of kerneltalks.
Feel free to use this system for testing your Linux
skills. In case of any issues reach out to admin at
info@kerneltalks.com. Thank you.

You don’t need to restart sshd daemon to take this change effect. As soon as you save the file, its content will be read and displayed by sshd daemon from the very next login request it serves.

You can see in the above screenshot: Yellow box is MOTD controlled by /etc/motd and the green box is what we saw earlier login banner.

You can use tools like cowsay, banner, figlet, lolcat to create fancy, eye-catching messages to display at login. This method works on almost all Linux distros like RedHat, Centos, Ubuntu, Fedora, etc.

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 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 –

name is Name you provide or hostname by default
caseID if you provide or blank
Date in yyyymmdd format
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.

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.

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 :

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.

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) $(MAINCC)
checking for GNU ld... yes
checking for inline... inline
checking for --enable-shared... no
checking for --enable-profiling... no
checking LDLIBRARY... libpython$(VERSION)$(ABIFLAGS).a
checking for ranlib... ranlib
checking for ar... ar
checking for readelf... readelf
checking for a BSD-compatible install... /bin/install -c
checking for a thread-safe mkdir -p... /bin/mkdir -p
checking for --with-pydebug... no
checking for --with-assertions... no
checking for --enable-optimizations... no
checking for --with-lto... no
checking target system type... x86_64-pc-linux-gnu
checking for -llvm-profdata... no
checking for llvm-profdata... ''
checking for -Wextra... yes
checking whether gcc accepts and needs -fno-strict-aliasing... no
checking if we can turn off gcc unused result warning... yes
checking if we can turn off gcc unused parameter warning... yes
checking if we can turn off gcc missing field initializers warning... yes
checking if we can turn on gcc mixed sign comparison warning... yes
checking if we can turn on gcc unreachable code warning... no
checking whether pthreads are available without options... no
checking whether gcc accepts -Kpthread... no
checking whether gcc accepts -Kthread... no
checking whether gcc accepts -pthread... yes
checking whether g++ also accepts flags for thread support... no
checking for ANSI C header files... (cached) yes
checking asm/types.h usability... yes
checking asm/types.h presence... yes
checking for asm/types.h... yes
checking conio.h usability... no
checking conio.h presence... no
checking for conio.h... no
checking direct.h usability... no
checking direct.h presence... no
checking for direct.h... no
checking dlfcn.h usability... yes
checking dlfcn.h presence... yes
checking for dlfcn.h... yes
checking errno.h usability... yes
checking errno.h presence... yes
checking for errno.h... yes
checking fcntl.h usability... yes
checking fcntl.h presence... yes
checking for fcntl.h... yes
checking grp.h usability... yes
checking grp.h presence... yes
checking for grp.h... yes
checking ieeefp.h usability... no
checking ieeefp.h presence... no
checking for ieeefp.h... no
checking io.h usability... no
checking io.h presence... no
checking for io.h... no
checking langinfo.h usability... yes
checking langinfo.h presence... yes
checking for langinfo.h... yes
checking libintl.h usability... yes
checking libintl.h presence... yes
checking for libintl.h... yes
checking process.h usability... no
checking process.h presence... no
checking for process.h... no
checking pthread.h usability... yes
checking pthread.h presence... yes
checking for pthread.h... yes
checking sched.h usability... yes
checking sched.h presence... yes
checking for sched.h... yes
checking shadow.h usability... yes
checking shadow.h presence... yes
checking for shadow.h... yes
checking signal.h usability... yes
checking signal.h presence... yes
checking for signal.h... yes
checking stropts.h usability... no
checking stropts.h presence... no
checking for stropts.h... no
checking termios.h usability... yes
checking termios.h presence... yes
checking for termios.h... yes
checking for unistd.h... (cached) yes
checking utime.h usability... yes
checking utime.h presence... yes
checking for utime.h... yes
checking poll.h usability... yes
checking poll.h presence... yes
checking for poll.h... yes
checking sys/devpoll.h usability... no
checking sys/devpoll.h presence... no
checking for sys/devpoll.h... no
checking sys/epoll.h usability... yes
checking sys/epoll.h presence... yes
checking for sys/epoll.h... yes
checking sys/poll.h usability... yes
checking sys/poll.h presence... yes
checking for sys/poll.h... yes
checking sys/audioio.h usability... no
checking sys/audioio.h presence... no
checking for sys/audioio.h... no
checking sys/xattr.h usability... yes
checking sys/xattr.h presence... yes
checking for sys/xattr.h... yes
checking sys/bsdtty.h usability... no
checking sys/bsdtty.h presence... no
checking for sys/bsdtty.h... no
checking sys/event.h usability... no
checking sys/event.h presence... no
checking for sys/event.h... no
checking sys/file.h usability... yes
checking sys/file.h presence... yes
checking for sys/file.h... yes
checking sys/ioctl.h usability... yes
checking sys/ioctl.h presence... yes
checking for sys/ioctl.h... yes
checking sys/kern_control.h usability... no
checking sys/kern_control.h presence... no
checking for sys/kern_control.h... no
checking sys/loadavg.h usability... no
checking sys/loadavg.h presence... no
checking for sys/loadavg.h... no
checking sys/lock.h usability... no
checking sys/lock.h presence... no
checking for sys/lock.h... no
checking sys/mkdev.h usability... no
checking sys/mkdev.h presence... no
checking for sys/mkdev.h... no
checking sys/modem.h usability... no
checking sys/modem.h presence... no
checking for sys/modem.h... no
checking sys/param.h usability... yes
checking sys/param.h presence... yes
checking for sys/param.h... yes
checking sys/random.h usability... no
checking sys/random.h presence... no
checking for sys/random.h... no
checking sys/select.h usability... yes
checking sys/select.h presence... yes
checking for sys/select.h... yes
checking sys/sendfile.h usability... yes
checking sys/sendfile.h presence... yes
checking for sys/sendfile.h... yes
checking sys/socket.h usability... yes
checking sys/socket.h presence... yes
checking for sys/socket.h... yes
checking sys/statvfs.h usability... yes
checking sys/statvfs.h presence... yes
checking for sys/statvfs.h... yes
checking for sys/stat.h... (cached) yes
checking sys/syscall.h usability... yes
checking sys/syscall.h presence... yes
checking for sys/syscall.h... yes
checking sys/sys_domain.h usability... no
checking sys/sys_domain.h presence... no
checking for sys/sys_domain.h... no
checking sys/termio.h usability... no
checking sys/termio.h presence... no
checking for sys/termio.h... no
checking sys/time.h usability... yes
checking sys/time.h presence... yes
checking for sys/time.h... yes
checking sys/times.h usability... yes
checking sys/times.h presence... yes
checking for sys/times.h... yes
checking for sys/types.h... (cached) yes
checking sys/uio.h usability... yes
checking sys/uio.h presence... yes
checking for sys/uio.h... yes
checking sys/un.h usability... yes
checking sys/un.h presence... yes
checking for sys/un.h... yes
checking sys/utsname.h usability... yes
checking sys/utsname.h presence... yes
checking for sys/utsname.h... yes
checking sys/wait.h usability... yes
checking sys/wait.h presence... yes
checking for sys/wait.h... yes
checking pty.h usability... yes
checking pty.h presence... yes
checking for pty.h... yes
checking libutil.h usability... no
checking libutil.h presence... no
checking for libutil.h... no
checking sys/resource.h usability... yes
checking sys/resource.h presence... yes
checking for sys/resource.h... yes
checking netpacket/packet.h usability... yes
checking netpacket/packet.h presence... yes
checking for netpacket/packet.h... yes
checking sysexits.h usability... yes
checking sysexits.h presence... yes
checking for sysexits.h... yes
checking bluetooth.h usability... no
checking bluetooth.h presence... no
checking for bluetooth.h... no
checking linux/tipc.h usability... yes
checking linux/tipc.h presence... yes
checking for linux/tipc.h... yes
checking linux/random.h usability... yes
checking linux/random.h presence... yes
checking for linux/random.h... yes
checking spawn.h usability... yes
checking spawn.h presence... yes
checking for spawn.h... yes
checking util.h usability... no
checking util.h presence... no
checking for util.h... no
checking alloca.h usability... yes
checking alloca.h presence... yes
checking for alloca.h... yes
checking endian.h usability... yes
checking endian.h presence... yes
checking for endian.h... yes
checking sys/endian.h usability... no
checking sys/endian.h presence... no
checking for sys/endian.h... no
checking sys/sysmacros.h usability... yes
checking sys/sysmacros.h presence... yes
checking for sys/sysmacros.h... yes
checking for dirent.h that defines DIR... yes
checking for library containing opendir... none required
checking whether sys/types.h defines makedev... yes
checking bluetooth/bluetooth.h usability... no
checking bluetooth/bluetooth.h presence... no
checking for bluetooth/bluetooth.h... no
checking for net/if.h... yes
checking for linux/netlink.h... yes
checking for linux/can.h... yes
checking for linux/can/raw.h... yes
checking for linux/can/bcm.h... yes
checking for clock_t in time.h... yes
checking for makedev... yes
checking for le64toh... yes
checking Solaris LFS bug... no
checking for mode_t... yes
checking for off_t... yes
checking for pid_t... yes
checking for size_t... yes
checking for uid_t in sys/types.h... yes
checking for ssize_t... yes
checking for __uint128_t... yes
checking size of int... 4
checking size of long... 8
checking size of long long... 8
checking size of void *... 8
checking size of short... 2
checking size of float... 4
checking size of double... 8
checking size of fpos_t... 16
checking size of size_t... 8
checking size of pid_t... 4
checking size of uintptr_t... 8
checking for long double support... yes
checking size of long double... 16
checking size of _Bool... 1
checking size of off_t... 8
checking whether to enable large file support... no
checking size of time_t... 8
checking for pthread_t... yes
checking size of pthread_t... 8
checking for --enable-framework... no
checking for dyld... no
checking the extension of shared libraries... .so
checking LDSHARED... $(CC) -shared
checking CCSHARED... -fPIC
checking LINKFORSHARED... -Xlinker -export-dynamic
checking CFLAGSFORSHARED...
checking SHLIBS... $(LIBS)
checking for sendfile in -lsendfile... no
checking for dlopen in -ldl... yes
checking for shl_load in -ldld... no
checking for library containing sem_init... -lpthread
checking for textdomain in -lintl... no
checking aligned memory access is required... no
checking for --with-hash-algorithm... default
checking for --with-address-sanitizer... no
checking for t_open in -lnsl... no
checking for socket in -lsocket... no
checking for --with-libs... no
checking for pkg-config... /bin/pkg-config
checking pkg-config is at least version 0.9.0... yes
checking for --with-system-expat... no
checking for --with-system-ffi... yes
checking for --with-system-libmpdec... no
checking for --enable-loadable-sqlite-extensions... no
checking for --with-tcltk-includes... default
checking for --with-tcltk-libs... default
checking for --with-dbmliborder...
checking for --with-threads... yes
checking if PTHREAD_SCOPE_SYSTEM is supported... yes
checking for pthread_sigmask... yes
checking for pthread_atfork... yes
checking if --enable-ipv6 is specified... yes
checking if RFC2553 API is available... yes
checking ipv6 stack type... linux-glibc
checking for CAN_RAW_FD_FRAMES... yes
checking for --with-doc-strings... yes
checking for --with-pymalloc... yes
checking for --with-valgrind... no
checking for --with-dtrace... no
checking for dlopen... yes
checking DYNLOADFILE... dynload_shlib.o
checking MACHDEP_OBJS... none
checking for alarm... yes
checking for accept4... yes
checking for setitimer... yes
checking for getitimer... yes
checking for bind_textdomain_codeset... yes
checking for chown... yes
checking for clock... yes
checking for confstr... yes
checking for ctermid... yes
checking for dup3... yes
checking for execv... yes
checking for faccessat... yes
checking for fchmod... yes
checking for fchmodat... yes
checking for fchown... yes
checking for fchownat... yes
checking for fexecve... yes
checking for fdopendir... yes
checking for fork... yes
checking for fpathconf... yes
checking for fstatat... yes
checking for ftime... yes
checking for ftruncate... yes
checking for futimesat... yes
checking for futimens... yes
checking for futimes... yes
checking for gai_strerror... yes
checking for getentropy... no
checking for getgrouplist... yes
checking for getgroups... yes
checking for getlogin... yes
checking for getloadavg... yes
checking for getpeername... yes
checking for getpgid... yes
checking for getpid... yes
checking for getpriority... yes
checking for getresuid... yes
checking for getresgid... yes
checking for getpwent... yes
checking for getspnam... yes
checking for getspent... yes
checking for getsid... yes
checking for getwd... yes
checking for initgroups... yes
checking for kill... yes
checking for killpg... yes
checking for lchmod... no
checking for lchown... yes
checking for linkat... yes
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checking for sem_unlink... yes
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checking for ctermid_r... no
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checking for broken unsetenv... no
checking for true... true
checking for inet_aton in -lc... yes
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checking for inflateCopy in -lz... no
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checking digit size for Python's longs... no value specified
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checking size of wchar_t... 4
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no usable wchar_t found
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checking SOABI... cpython-36m-x86_64-linux-gnu
checking LDVERSION... $(VERSION)$(ABIFLAGS)
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configure: checking for device files
checking for /dev/ptmx... yes
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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?

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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.

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 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!