Author Archives: LinuxTech

error: Failed to create domain from /etc/libvirt/qemu/

We had a issue in one of the virtualizor node

Where the server on rebooting the KVM VM were not starting

With error message being

error: Failed to create domain from /etc/libvirt/qemu/
error: Cannot get interface MTU on ‘viifbr0’: No such device

ON checking around found the issue with virtnetwork

Below command fixed the issue

service virtnetwork start

~]# service virtnetwork start
Bringing up viifbr0 – OK
Waiting for 10 seconds…1…2…3…4…5…6…7…8…9…10
Internet connectivity check successful viifbr0 – OK

Open port in Centos 7

Below are the commands which are to be used in centos 7 to open port 80

[root@onlinesupport ~]# firewall-cmd --permanent --zone=public --add-port=80/tcp success

[root@onlinesupport]# firewall-cmd --reload

Mysql Upgrade Process

While upgrading mysql in server make sure you make a backup of existing mysql

using commmand mysqldump --all-databases > all_databases.sql

Once you have complete backup , You can proceed with with upgrade of mysql.

/tmp is 100% due to Mysql

Was having an issue where /tmp was getting 100% full every few minutes

on investigation i see the files of 3Gb over there in /tmp


ddvps20 tmp]# ls -al
total 3779332
drwxrwxrwt 12 root root 4096 Sep 21 10:24 .
dr-xr-xr-x 21 root root 4096 Sep 21 09:17 ..
drwxrwxrwt 2 root root 4096 Sep 21 09:17 .font-unix
drwxr-xr-x 2 cpanelsolr cpanelsolr 4096 Sep 21 10:22 hsperfdata_cpanelsolr
drwxr-xr-x 2 root root 4096 Sep 21 10:21 hsperfdata_root
drwxrwxrwt 2 root root 4096 Sep 21 09:17 .ICE-unix
drwx—— 2 root root 16384 Sep 21 09:56 lost+found
lrwxrwxrwx 1 root root 30 Sep 21 10:23 mysql.sock -> ../../var/lib/mysql/mysql.sock
-rw——- 1 cpdigita cpdigita 4096 Sep 21 10:11 .spamassassin1694OHMO4Dtmp
-rw——- 1 cpdigita cpdigita 0 Sep 21 10:17 .spamassassin1694voSq6Ctmp
-rw——- 1 cpdigita cpdigita 0 Sep 21 10:11 .spamassassin1694y0CJyjtmp
-rw——- 1 cpdigita cpdigita 0 Sep 21 10:04 .spamassassin18453ZHMaRtmp
-rw——- 1 cpdigita cpdigita 0 Sep 21 10:06 .spamassassin1845bypIDCtmp
-rw——- 1 cpdigita cpdigita 0 Sep 21 10:03 .spamassassin1845pCtlHqtmp
-rw-rw—- 1 mysql mysql 3866185728 Sep 21 10:07 #sql_436_0.MAD
-rw-rw—- 1 mysql mysql 8192 Sep 21 10:00 #sql_436_0.MAI
-rw——- 1 cpanelsolr cpanelsolr 165 Sep 21 10:22
drwx—— 3 root root 4096 Sep 21 09:17 systemd-private-1d4af49159364e018772426d7df23a9d-named.service-8XVCsj
drwx—— 3 root root 4096 Sep 21 09:17 systemd-private-1d4af49159364e018772426d7df23a9d-named.service-FyUDBs
drwxrwxrwt 2 root root 4096 Sep 21 09:17 .Test-unix
drwxrwxrwt 2 root root 4096 Sep 21 09:17 .X11-unix
drwxrwxrwt 2 root root 4096 Sep 21 09:17 .XIM-unix

So mysql was going down due to /tmp being full

So as a work around found a better solution

To change the /tmp file to something else for mysql

vi /etc/my.cnf

Save the file with :wq

2. Create the /mysqltmp directory

mkdir /mysqltmp
chmod 1777 /mysqltmp

3. Restart MySQL and check that the tmpdir is now /mysqltmp
/etc/init.d/mysql restart
mysqladmin var | grep tmpdir
You should see the following return:

# mysqladmin var | grep tmpdir
| slave_load_tmpdir                       | /mysqltmp
| tmpdir                                  | /mysqltmp

Redirecting HTTP to HTTPS

Redirecting HTTP to HTTPS

RewriteEngine On
RewriteCond %{SERVER_PORT} 80
RewriteRule ^(.*)$$1 [R,L]

Redirect Only a Specific Domain

RewriteEngine On
RewriteCond %{HTTP_HOST} ^yourdomain\.com [NC]
RewriteCond %{SERVER_PORT} 80
RewriteRule ^(.*)$$1 [R,L]
Redirecting to HTTPS on a specific folder, add the following:

[ERROR] Can’t init tc log Mariadb

2018-03-30 2:06:19 139671858284288 [Note] InnoDB: Dumping buffer pool(s) not yet started
2018-03-30 2:06:19 139672598403328 [Note] Plugin ‘FEEDBACK’ is disabled.
2018-03-30 2:06:19 139672598403328 [Note] Recovering after a crash using tc.log
2018-03-30 2:06:19 139672598403328 [ERROR] Can’t init tc log
2018-03-30 2:06:19 139672598403328 [ERROR] Aborting

Was getting above error in mysql errorlog

The solution to this issue was just to go ahead and delete tc.log

rm -rf /var/lib/mysql/tc.log

Went ahead and restart mysql.. Mysql was online

root@server lib]# rm -rf /var/lib/mysql/tc.log
[root@server lib]# /etc/init.d/mysql restart
MySQL server PID file could not be found! [FAILED]
Starting MySQL.180330 02:07:40 mysqld_safe Logging to ‘/var/lib/mysql/’.
180330 02:07:40 mysqld_safe Starting mysqld daemon with databases from /var/lib/mysql
[ OK ]
[root@server lib]#


Column count of mysql.user is wrong

Was getting below error while trying to create mysql user in cpanel

Error from MySQL query :(XID 5yuvwf) The system received an error from the “MySQL” database “mysql”: 1805 (Column count of mysql.user is wrong. Expected 43, found 39. The table is probably corrupted):

The migration used a “mysqldump –all-databases” so it included the “mysql” database. Apparently the “mysql.proc” table changed between the versions. The fix on the new server is to run:


Below command fixed the issue

mysql_upgrade force


Windows OS not visible on dual boot

We had attempted a dual boot vps on KVM based vps

The os were installed using ISO

First to start with windows and then linux

However after installing linux the windows OS went missing

ON googling around found a solution

The issue was due to missing modules where we had to install module  ntfs-3g

[root@ohours ~]# yum install ntfs-3g
Loaded plugins: fastestmirror
base                                                                                                                                                                                 | 3.6 kB  00:00:00
extras                                                                                                                                                                               | 3.4 kB  00:00:00
updates                                                                                                                                                                              | 3.4 kB  00:00:00
(1/4): base/7/x86_64/group_gz                                                                                                                                                        | 156 kB  00:00:00
(2/4): extras/7/x86_64/primary_db                                                                                                                                                    | 167 kB  00:00:00
(3/4): updates/7/x86_64/primary_db                                                                                                                                                   | 6.0 MB  00:00:00
(4/4): base/7/x86_64/primary_db                                                                                                                                                      | 5.7 MB  00:00:01
Determining fastest mirrors
* base:
* extras:
* updates:
No package ntfs-3g available.
Error: Nothing to do

we  had to use epel repository to install  ntfs-3g as its not available with normal repository

#Command to enable epel repository

[root@ohours ~]# yum install epel-release
Loaded plugins: fastestmirror
Loading mirror speeds from cached hostfile
* base:
* extras:
* updates:
Resolving Dependencies
–> Running transaction check
—> Package epel-release.noarch 0:7-9 will be installed
–> Finished Dependency Resolution

Dependencies Resolved

Package                                               Arch                                            Version                                        Repository                                       Size
epel-release                                          noarch                                          7-9                                            extras                                           14 k

Transaction Summary
Install  1 Package

Total download size: 14 k
Installed size: 24 k
Is this ok [y/d/N]: y
Downloading packages:
warning: /var/cache/yum/x86_64/7/extras/packages/epel-release-7-9.noarch.rpm: Header V3 RSA/SHA256 Signature, key ID f4a80eb5: NOKEY
Public key for epel-release-7-9.noarch.rpm is not installed
epel-release-7-9.noarch.rpm                                                                                                                                                          |  14 kB  00:00:00
Retrieving key from file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-7
Importing GPG key 0xF4A80EB5:
Userid     : “CentOS-7 Key (CentOS 7 Official Signing Key) <>”
Fingerprint: 6341 ab27 53d7 8a78 a7c2 7bb1 24c6 a8a7 f4a8 0eb5
Package    : centos-release-7-4.1708.el7.centos.x86_64 (@anaconda)
From       : /etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-7
Is this ok [y/N]: y
Running transaction check
Running transaction test
Transaction test succeeded
Running transaction
Installing : epel-release-7-9.noarch                                                                                                                                                                  1/1
Verifying  : epel-release-7-9.noarch                                                                                                                                                                  1/1

epel-release.noarch 0:7-9                                                                                                                                                                               


[root@ohours ~]# yum install ntfs-3g
Loaded plugins: fastestmirror
epel/x86_64/metalink                                                                                                                                                                 |  16 kB  00:00:00
epel                                                                                                                                                                                 | 4.7 kB  00:00:00
(1/3): epel/x86_64/group_gz                                                                                                                                                          | 266 kB  00:00:00
(2/3): epel/x86_64/updateinfo                                                                                                                                                        | 899 kB  00:00:00
(3/3): epel/x86_64/primary_db                                                                                                                                                        | 6.3 MB  00:00:00
Loading mirror speeds from cached hostfile
* base:
* epel:
* extras:
* updates:
Resolving Dependencies
–> Running transaction check
—> Package ntfs-3g.x86_64 2:2017.3.23-1.el7 will be installed
–> Finished Dependency Resolution

Dependencies Resolved

Package                                        Arch                                          Version                                                     Repository                                   Size
ntfs-3g                                        x86_64                                        2:2017.3.23-1.el7                                           epel                                        263 k

Transaction Summary
Install  1 Package

Total download size: 263 k
Installed size: 612 k
Is this ok [y/d/N]: y
Downloading packages:
warning: /var/cache/yum/x86_64/7/epel/packages/ntfs-3g-2017.3.23-1.el7.x86_64.rpm: Header V3 RSA/SHA256 Signature, key ID 352c64e5: NOKEY
Public key for ntfs-3g-2017.3.23-1.el7.x86_64.rpm is not installed
ntfs-3g-2017.3.23-1.el7.x86_64.rpm                                                                                                                                                   | 263 kB  00:00:00
Retrieving key from file:///etc/pki/rpm-gpg/RPM-GPG-KEY-EPEL-7
Importing GPG key 0x352C64E5:
Userid     : “Fedora EPEL (7) <>”
Fingerprint: 91e9 7d7c 4a5e 96f1 7f3e 888f 6a2f aea2 352c 64e5
Package    : epel-release-7-9.noarch (@extras)
From       : /etc/pki/rpm-gpg/RPM-GPG-KEY-EPEL-7
Is this ok [y/N]: y
Running transaction check
Running transaction test
Transaction test succeeded
Running transaction
Installing : 2:ntfs-3g-2017.3.23-1.el7.x86_64                                                                                                                                                         1/1
Verifying  : 2:ntfs-3g-2017.3.23-1.el7.x86_64                                                                                                                                                         1/1

ntfs-3g.x86_64 2:2017.3.23-1.el7                                                                                                                                                                   


#Using below command find the OS loaded in system

[root@ohours ~]# grub2-mkconfig > /dev/null
Generating grub configuration file …
Found linux image: /boot/vmlinuz-3.10.0-693.el7.x86_64
Found initrd image: /boot/initramfs-3.10.0-693.el7.x86_64.img
Found linux image: /boot/vmlinuz-0-rescue-4754405db1084b4e8d440c2aef41bef8
Found initrd image: /boot/initramfs-0-rescue-4754405db1084b4e8d440c2aef41bef8.img
Found Windows Recovery Environment (loader) on /dev/sda1

if windows is not found the OS may have got formatted while installing other OS

However our windows os was intact as the results show

#make backup copy of grub.conf

sudo cp /boot/grub2/grub.cfg /boot/grub2/grub.cfg.old

#Recreate  the grub.conf to load windows and linux os using below command

sudo grub2-mkconfig -o /boot/grub2/grub.cfg

and now reboot and see both OS load