Tag: CentOS 7

OVH CentOS 7 server grub rescue prompt

On an OVH Cpanel server running CentOS 7, the server won’t boot. When accessing the server console using IPMI, I found the following error.

I booted the server into rescue mode, checked the disk partitions with the command parted -l

Disk /dev/nvme0n1: 450GB
Sector size (logical/physical): 512B/512B
Partition Table: gpt
Disk Flags: 

Number  Start   End     Size    File system     Name     Flags
 1      1049kB  537MB   536MB   fat32           primary  boot, esp
 2      537MB   1073MB  536MB   ext4            primary  raid
 3      1073MB  53.5GB  52.4GB  ext4            primary  raid
 4      53.5GB  450GB   396GB   ext4            primary  raid
 5      450GB   450GB   536MB   linux-swap(v1)  primary


Disk /dev/nvme1n1: 450GB
Sector size (logical/physical): 512B/512B
Partition Table: gpt
Disk Flags: 

Number  Start   End     Size    File system     Name     Flags
 1      1049kB  537MB   536MB   fat32           primary  boot, esp
 2      537MB   1073MB  536MB   ext4            primary  raid
 3      1073MB  53.5GB  52.4GB  ext4            primary  raid
 4      53.5GB  450GB   396GB   ext4            primary  raid
 5      450GB   450GB   536MB   linux-swap(v1)  primary

The server had 2 NVMe disks configured as RAID 1 mirrors. The first partition with fat32 filesystem is used for boot.

To fix the problem, I chrooted to the server file system with the following command (this may be changed based on your server’s partition scheme).

mount /dev/md3 /mnt
mount /dev/md2 /mnt/boot/
mount /dev/md4 /mnt/home
mount --bind /dev /mnt/dev
mount --bind /sys /mnt/sys
mount --bind /proc /mnt/proc
mount --bind /dev/pts /mnt/dev/pts/
chroot /mnt

Reinstalled the kernel with

yum reinstall kernel

Then reinstalled grub loader. This server used UEFI, so used following commands

mkdir /nvme0n1p1
mkdir /nvme1n1p1
mount /dev/nvme0n1p1 /nvme0n1p1
mount /dev/nvme1n1p1 /nvme1n1p1
grub2-install --target=x86_64-efi --efi-directory=/nvme0n1p1 --bootloader-id=GRUB
grub2-install --target=x86_64-efi --efi-directory=/nvme1n1p1 --bootloader-id=GRUB

grub boot loaded is installed on both disks, so server will be able to boot when either one of the disk is selected as boot device.

Back to grub

January 4, 2023

How to reset CentOS 7 root password using console
If you have lost the root password of your CentOS 7 system and have access to the console directly or using KVM, you can reset the password following the instructions below.

1) Reboot the server, you will see the grub menu.

2) Press “e” to edit. You will see the edit screen as shown below.

3) Find the line starting with linux16
```
linux16 /boot/vmlinuz-3.10.0-1160.76.1.el7.x86_64 root=UUID=1c419d6c-5064-4a2b-953c-05b2c67edb15 ro no_timer_check console=tty0 console=ttyS0,115200n8 net.ifnames=0 biosdevname=0 elevator=noop crashkernel=auto LANG=en_US.UTF-8
```
In the fine, find
```
ro
```
Delete everything after that and replace with “rd.break”, so the line looks like the following
```
linux16 /boot/vmlinuz-3.10.0-1160.76.1.el7.x86_64 root=UUID=1c419d6c-5064-4a2b-953c-05b2c67edb15 ro rd.break
```
4) Boot the system to the emergency mode by pressing CTRL + X, you will get a prompt like the following

5) Mount /sysroot in read-write mode. and chroot to the file system
```
mount -o remount,rw /sysroot
chroot /sysroot
```
6) Reset the root password with passwd command
```
passwd
```
7) SELinux won’t allow modifying system files like /etc/shadow, to allow the change, create a file
```
touch /.autorelabel
```
7) Now reboot the system by typing the “exit” command two times
```
exit
exit
```
After rebooting, you will be able to log in to the system with the new root password.

Back to CentOS 7
November 8, 2022

Install PHP APC Cache on CentOS 7 using yum

To install APC cache on CentOS 7, run

yum install php-pecl-apcu

After that, you need to restart the Apache webserver.

systemctl restart httpd

in phpinfo() page, you will see

Files in the packages are

[root@localhost ~]# rpm -q --filesbypkg  php-pecl-apcu
php-pecl-apcu             /etc/php-zts.d/40-apcu.ini
php-pecl-apcu             /etc/php.d/40-apcu.ini
php-pecl-apcu             /usr/lib64/php-zts/modules/apcu.so
php-pecl-apcu             /usr/lib64/php/modules/apcu.so
php-pecl-apcu             /usr/share/doc/pecl/apcu
php-pecl-apcu             /usr/share/doc/pecl/apcu/NOTICE
php-pecl-apcu             /usr/share/doc/pecl/apcu/README.md
php-pecl-apcu             /usr/share/doc/pecl/apcu/TECHNOTES.txt
php-pecl-apcu             /usr/share/licenses/php-pecl-apcu-5.1.21
php-pecl-apcu             /usr/share/licenses/php-pecl-apcu-5.1.21/LICENSE
php-pecl-apcu             /var/lib/pear/pkgxml/php-pecl-apcu.xml
[root@localhost ~]#

Config file located at

/etc/php.d/40-apcu.ini

Some configuration settings

apc.shm_size – default is 64M, it is better increase this value to 128M

apc.stat – default 1, set it to 0 to increase performance. Setting it to 0 means APC won’t look for code change. When you change code, you will need to restart web server.

apc.num_files_hint – Tell APC how many PHP files it needs to cache. Set it to 10000

December 26, 2021

Install Tomcat on CentOS 7

Apache Tomcat is an open source implementation of the Java Servlet and Java Server Pages. To install Apache Tomcat on CentOS 7, run

yum install tomcat

To enable tomcat start on boot

systemctl enable tomcat

You can manage tomcat with

systemctl stop tomcat
systemctl start tomcat
systemctl status tomcat
systemctl restart tomcat

To see the ports used by tomcat

[root@tomcat ~]# netstat -lntp| grep java
tcp6       0      0 127.0.0.1:8005          :::*                    LISTEN      31423/java          
tcp6       0      0 :::8009                 :::*                    LISTEN      31423/java          
tcp6       0      0 :::8080                 :::*                    LISTEN      31423/java          
[root@tomcat ~]#

webapps are stored in the directory

/var/lib/tomcat/webapps

Create the default page with

mkdir /var/lib/tomcat/webapps/ROOT
echo "Hello Cat" > /var/lib/tomcat/webapps/ROOT/index.html

Tomcat web server can be accessed using

http://your-server-ip:8080

To open 8080 port on the firewall, use commands

firewall-cmd --permanent --zone=public --add-port=8080/tcp
firewall-cmd --reload

Tomcat configurations are available in the directory.

/etc/tomcat/

Install tomcat Manager

To install the Tomcat manager GUI application, run

yum install tomcat-admin-webapps.noarch -y

To create user, edit file

vi /etc/tomcat/tomcat-users.xml

Inside ““, add

USER_NAME_HERE and PW_HERE – replace with the username and password you need.

Restart tomcat to activate Tomcat Manager GUI.

systemctl restart tomcat

To access GUI, go to

http://your-server-ip-here:8080/manager/

November 2, 2021

Elasticsearch failed to start on CentOS 7

After installing elasticsearch on CentOS 7, it failed to start with error

[root@ns3160182 ~]# systemctl start elasticsearch.service

Job for elasticsearch.service failed because the control process exited with error code. See "systemctl status elasticsearch.service" and "journalctl -xe" for details.
[root@ns3160182 ~]# 
[root@ns3160182 ~]# systemctl status elasticsearch.service
● elasticsearch.service - Elasticsearch
   Loaded: loaded (/usr/lib/systemd/system/elasticsearch.service; enabled; vendor preset: disabled)
   Active: failed (Result: exit-code) since Sat 2021-03-06 11:10:24 CET; 28s ago
     Docs: https://www.elastic.co
  Process: 10234 ExecStart=/usr/share/elasticsearch/bin/systemd-entrypoint -p ${PID_DIR}/elasticsearch.pid --quiet (code=exited, status=1/FAILURE)
 Main PID: 10234 (code=exited, status=1/FAILURE)
   CGroup: /system.slice/elasticsearch.service

Mar 06 11:10:24 ns3160182.ip-151-106-34.eu systemd-entrypoint[10234]: at org.elasticsearch.bootstrap.Elasticsearch.execute(Elasticsearch.java:161)
Mar 06 11:10:24 ns3160182.ip-151-106-34.eu systemd-entrypoint[10234]: at org.elasticsearch.cli.EnvironmentAwareCommand.execute(EnvironmentAwareCommand.java:86)
Mar 06 11:10:24 ns3160182.ip-151-106-34.eu systemd-entrypoint[10234]: at org.elasticsearch.cli.Command.mainWithoutErrorHandling(Command.java:127)
Mar 06 11:10:24 ns3160182.ip-151-106-34.eu systemd-entrypoint[10234]: at org.elasticsearch.cli.Command.main(Command.java:90)
Mar 06 11:10:24 ns3160182.ip-151-106-34.eu systemd-entrypoint[10234]: at org.elasticsearch.bootstrap.Elasticsearch.main(Elasticsearch.java:126)
Mar 06 11:10:24 ns3160182.ip-151-106-34.eu systemd-entrypoint[10234]: at org.elasticsearch.bootstrap.Elasticsearch.main(Elasticsearch.java:92)
Mar 06 11:10:24 ns3160182.ip-151-106-34.eu systemd[1]: elasticsearch.service: main process exited, code=exited, status=1/FAILURE
Mar 06 11:10:24 ns3160182.ip-151-106-34.eu systemd[1]: Failed to start Elasticsearch.
Mar 06 11:10:24 ns3160182.ip-151-106-34.eu systemd[1]: Unit elasticsearch.service entered failed state.
Mar 06 11:10:24 ns3160182.ip-151-106-34.eu systemd[1]: elasticsearch.service failed.
[root@ns3160182 ~]#

On checking journalctl, i get

[root@ns3160182 ~]# journalctl -u elasticsearch
-- Logs begin at Sat 2021-02-13 16:48:02 CET, end at Sat 2021-03-06 11:12:02 CET. --
Mar 06 11:10:01 ns3160182.ip-151-106-34.eu systemd[1]: Starting Elasticsearch...
Mar 06 11:10:24 ns3160182.ip-151-106-34.eu systemd-entrypoint[10234]: fatal error in thread [main], exiting
Mar 06 11:10:24 ns3160182.ip-151-106-34.eu systemd-entrypoint[10234]: java.lang.NoClassDefFoundError: Could not initialize class com.sun.jna.Native
Mar 06 11:10:24 ns3160182.ip-151-106-34.eu systemd-entrypoint[10234]: at org.elasticsearch.systemd.Libsystemd.lambda$static$0(Libsystemd.java:34)
Mar 06 11:10:24 ns3160182.ip-151-106-34.eu systemd-entrypoint[10234]: at java.base/java.security.AccessController.doPrivileged(AccessController.java:312)
Mar 06 11:10:24 ns3160182.ip-151-106-34.eu systemd-entrypoint[10234]: at org.elasticsearch.systemd.Libsystemd.(Libsystemd.java:33)
Mar 06 11:10:24 ns3160182.ip-151-106-34.eu systemd-entrypoint[10234]: at org.elasticsearch.systemd.SystemdPlugin.sd_notify(SystemdPlugin.java:126)
Mar 06 11:10:24 ns3160182.ip-151-106-34.eu systemd-entrypoint[10234]: at org.elasticsearch.systemd.SystemdPlugin.onNodeStarted(SystemdPlugin.java:137)
Mar 06 11:10:24 ns3160182.ip-151-106-34.eu systemd-entrypoint[10234]: at java.base/java.util.ArrayList.forEach(ArrayList.java:1511)
Mar 06 11:10:24 ns3160182.ip-151-106-34.eu systemd-entrypoint[10234]: at org.elasticsearch.node.Node.start(Node.java:902)
Mar 06 11:10:24 ns3160182.ip-151-106-34.eu systemd-entrypoint[10234]: at org.elasticsearch.bootstrap.Bootstrap.start(Bootstrap.java:317)
Mar 06 11:10:24 ns3160182.ip-151-106-34.eu systemd-entrypoint[10234]: at org.elasticsearch.bootstrap.Bootstrap.init(Bootstrap.java:402)
Mar 06 11:10:24 ns3160182.ip-151-106-34.eu systemd-entrypoint[10234]: at org.elasticsearch.bootstrap.Elasticsearch.init(Elasticsearch.java:170)
Mar 06 11:10:24 ns3160182.ip-151-106-34.eu systemd-entrypoint[10234]: at org.elasticsearch.bootstrap.Elasticsearch.execute(Elasticsearch.java:161)
Mar 06 11:10:24 ns3160182.ip-151-106-34.eu systemd-entrypoint[10234]: at org.elasticsearch.cli.EnvironmentAwareCommand.execute(EnvironmentAwareCommand.java:86)
Mar 06 11:10:24 ns3160182.ip-151-106-34.eu systemd-entrypoint[10234]: at org.elasticsearch.cli.Command.mainWithoutErrorHandling(Command.java:127)
Mar 06 11:10:24 ns3160182.ip-151-106-34.eu systemd-entrypoint[10234]: at org.elasticsearch.cli.Command.main(Command.java:90)
Mar 06 11:10:24 ns3160182.ip-151-106-34.eu systemd-entrypoint[10234]: at org.elasticsearch.bootstrap.Elasticsearch.main(Elasticsearch.java:126)
Mar 06 11:10:24 ns3160182.ip-151-106-34.eu systemd-entrypoint[10234]: at org.elasticsearch.bootstrap.Elasticsearch.main(Elasticsearch.java:92)
Mar 06 11:10:24 ns3160182.ip-151-106-34.eu systemd[1]: elasticsearch.service: main process exited, code=exited, status=1/FAILURE
Mar 06 11:10:24 ns3160182.ip-151-106-34.eu systemd[1]: Failed to start Elasticsearch.
Mar 06 11:10:24 ns3160182.ip-151-106-34.eu systemd[1]: Unit elasticsearch.service entered failed state.
Mar 06 11:10:24 ns3160182.ip-151-106-34.eu systemd[1]: elasticsearch.service failed.
[root@ns3160182 ~]#

To fix this, edit file

vi /etc/sysconfig/elasticsearch

At end of the file, add

ES_TMPDIR=/var/log/elasticsearch

Now elasticsearch will start

systemctl start elasticsearch

Verify service is running with

systemctl status elasticsearch

To confirm elasticsearch is running, use command

curl localhost:9200

See elasticsearch

March 6, 2021

Install Latest MariaDB on CentOS
To install the latest MariaDB on the CentOS server, go to

https://mariadb.org/download/?t=repo-config

On this page, select CentOS, then select your CentOS version and MariaDB version you need.

Below you will see instructions for your specific version of CentOS.

Install MariaDB 10.5 on CentOS 7

CentOS 7 by default provide MariaDB 5.5. To install MariaDB 10.5

Create file
```
vi /etc/yum.repos.d/MariaDB.repo
```
Add
```
# MariaDB 10.5 CentOS repository list - created 2020-11-05 08:27 UTC
# http://downloads.mariadb.org/mariadb/repositories/
[mariadb]
name = MariaDB
baseurl = http://yum.mariadb.org/10.5/centos7-amd64
gpgkey=https://yum.mariadb.org/RPM-GPG-KEY-MariaDB
gpgcheck=1
```
Now you can install MariDB with command
```
yum install MariaDB-server MariaDB-client
```
To start MariaDB, run
```
systemctl start mariadb
```
You can replace start with stop/restart/status. To auto start MariaDB on boot, run
```
systemctl enable mariadb
```
See MySQL
November 5, 2020
Install python 3.6 on CentOS 7
CentOS 7 come with Python 2.7. To install python 3.6, first install the EPEL repo.
```
yum install epel-repo -y
```
Install IUS repo.

https://ius.io/setup

For CentOS 7, run
```
rpm -ivh https://centos7.iuscommunity.org/ius-release.rpm
```
Now you can install Python 3.6 with yum
```
yum install python36u python36u-pip -y
```
Python 3.6 binary will be available as “python3.6” and “pip3.6”
September 14, 2018
CentOS 7
- CentOS 7 yum update HTTP Error 404: Not found
- CentOS 7 access denied: tty ‘tty1’ is not secure
Reset root password
- How to reset CentOS 7 root password using console
Install Software on CentOS 7
Web Server
MySQL
Back to CentOS
March 27, 2018

Tag: CentOS 7

Install tomcat Manager

Install MariaDB 10.5 on CentOS 7

Reset root password

Install Software on CentOS 7

Web Server

MySQL