Category: CentOS

CentOS 8
CentOS 8 is a short-lived Linux distribution based on Red Hat Enterprise Linux (RHEL). Due to a change in policy, CentOS 8 had an early end of life on December 31, 2021.

If you are using CentOS 8, you can easily migrate to other RHEL based distributions like Alma Linux, RockyLinux or Oracle Linux.

CentOS will now provide CentOS 8 Stream, which is a rolling release Linux distribution. CentOS 8 Stream will position itself in the middle of Fedora and RHEL. It won’t be a copy of RHEL, instead, it will be used as a testing ground for RHEL. Newer versions of the software get released on CentOS 8 Stream, once it becomes stable, it will be included in RHEL.
September 26, 2019
Run Apache from command line
To start Apache from command line with out using a systemd service file or init script, run
```
/usr/sbin/httpd -DFOREGROUND
```
To stop Apache, press CTRL+C.

You can keep it running by running it inside screen or tmux.

See Apache
September 25, 2019
Download RPM package from yum repository
To download RPM file from yum repo, you need to install yum-utils package.
```
yum install -y yum-utils
```
Now you can use command
```
yumdownloader --resolve --destdir=/path/ PACKAGE_NAME
```
Example
```
yumdownloader --resolve --destdir=/root/yum/ nginx
```
This will download and store all rpm files in /var/yum folder. –resolve will resolve dependency and download them. This will be helpful if you need to install a package on a system with no direct internet connection.

See yum
September 15, 2019
Setup Tor Hidden Service on CentOS 7
Tor is provided by EPEL repository on CentOS 7. Install EPEL repo with command
```
yum install epel-release
```
Install tor
```
yum install tor
```
Edit tor config file
```
vi /etc/tor/torrc
```
Uncomment or add following lines
```
HiddenServiceDir /var/lib/tor/hidden_service/
HiddenServicePort 80 127.0.0.1:80
```
Restart tor with command
```
systemctl restart tor
```
Now your tor hidden service is ready to use. You need to run your web application on 127.0.0.1:80

To see URL of your tor hidden service, run
```
cat /var/lib/tor/hidden_service/hostname
```
Make sure to make a backup of folder “/var/lib/tor/hidden_service/” as it comtains keys for this .onion domain. If you lost it, you will lose your domain name. So it is very important you keep the files safe.

To stop/start tor, run
```
systemctl stop tor
systemctl start tor
```
See tor
September 11, 2019

yum-config-manager

yum-config-manager allows you to manage yum repositories.

To add a repo, run

yum-config-manager --add-repo https://download.docker.com/linux/centos/docker-ce.repo

Disable a repository

yum-config-manager --disable rpmfusion-free-updates

See yum

August 9, 2019

CentOS add IP Address
To add IP address on a Linux server, first find name of your network interface. This can be done with command
```
ip link
```
In most case, it can be enp3s0 or eth0, if you have more than one network card, this may be differnt, in such case, you need to identify which network interface you need to configure the the IP address .

Now create file
```
vi /etc/sysconfig/network-scripts/ifcfg-enp3s0:1
```
Here i used enp3s0 as network inferface name, replace it with whatever network interface name you use.

Add following content
```
DEVICE="enp3s0:1"
IPADDR=IP_ADDR_HERE
NETMASK=255.255.255.255
```
IP_ADDR_HERE = replace with the IP address you need to add.

enp3s0 = replace with actual network interface name.

Restart network service with command
```
systemctl restart network
```
If you need to add another IP, create file with name
```
INTERFACE_NAME:2
```
for example “enp3s0:2”, you need to use same alias name in DEVICE entry (first line) in the file.

Adding IP Range in CentOS 6
August 5, 2019
Install vnstat on CentOS 7
To install vnstat on CentOS 7, run
```
yum install vnstat -y
```
Now create database for your network interface card
```
vnstat --create -i NETWORK_INTERFACE_NAME
```
Restart vnstat deamon
```
systemctl restart vnstat
```
See vnstat
July 15, 2019
Install Transmission on CentOS
transmission is a torrent client. This come with a web GUI, that make it easy to installed on a remote server with no X-Windows. To install transmission on CentOS server, run
```
yum install -y transmission-daemon transmission-cli
```
Allow Web Access

To access transmission web GUI, you need to white list your IP address. To do this, first stop tranmission
```
service transmission-daemon stop
```
Edit file
```
vi /var/lib/transmission/.config/transmission/settings.json
```
Find
```
    "rpc-whitelist": "127.0.0.1",
```
Replace with
```
    "rpc-whitelist": "127.0.0.1,YOUR_IP_ADDR_HERE",
```
YOUR_IP_ADDR_HERE – replace with your actual IP address.

Start transmission
```
service transmission-daemon start
```
You will be able to access web GUI at
```
http://YOUR_SERVER_IP:9091
```
Downloaded files are stored in folder
```
/var/lib/transmission/Downloads
```
July 5, 2019

Install MongoDB 4.0 on CentOS 7

To install MongoDB 4.0 (for other versions, see release note) on CentOS 7, create file

vi /etc/yum.repos.d/mongodb-org-4.0.repo

Add content

[mongodb-org-4.0]
name=MongoDB Repository
baseurl=https://repo.mongodb.org/yum/redhat/$releasever/mongodb-org/4.0/x86_64/
gpgcheck=1
enabled=1
gpgkey=https://www.mongodb.org/static/pgp/server-4.0.asc

Install MongoDB with

yum install -y mongodb-org

Enable MongoDB start on boot

systemctl enable mongod

Start Mongo DB with

systemctl start mongod

To see mongoDB version, run

[root@ns3084948 ~]# mongo --version
MongoDB shell version v4.0.10
git version: c389e7f69f637f7a1ac3cc9fae843b635f20b766
OpenSSL version: OpenSSL 1.0.1e-fips 11 Feb 2013
allocator: tcmalloc
modules: none
build environment:
    distmod: rhel70
    distarch: x86_64
    target_arch: x86_64
[root@ns3084948 ~]#

To see if mongoDB running

[root@ns3084948 ~]# netstat -lntp | grep mongo
tcp        0      0 127.0.0.1:27017         0.0.0.0:*               LISTEN      10349/mongod        
[root@ns3084948 ~]#

Or use

[root@ns3084948 ~]# systemctl status mongod
● mongod.service - MongoDB Database Server
   Loaded: loaded (/usr/lib/systemd/system/mongod.service; enabled; vendor preset: disabled)
   Active: active (running) since Tue 2019-06-04 06:08:01 BST; 18min ago
     Docs: https://docs.mongodb.org/manual
  Process: 10347 ExecStart=/usr/bin/mongod $OPTIONS (code=exited, status=0/SUCCESS)
  Process: 10344 ExecStartPre=/usr/bin/chmod 0755 /var/run/mongodb (code=exited, status=0/SUCCESS)
  Process: 10341 ExecStartPre=/usr/bin/chown mongod:mongod /var/run/mongodb (code=exited, status=0/SUCCESS)
  Process: 10338 ExecStartPre=/usr/bin/mkdir -p /var/run/mongodb (code=exited, status=0/SUCCESS)
 Main PID: 10349 (mongod)
   Memory: 46.7M
   CGroup: /system.slice/mongod.service
           └─10349 /usr/bin/mongod -f /etc/mongod.conf

Jun 04 06:07:57 ns3084948.ip-145-239-4.eu systemd[1]: Starting MongoDB Database Server...
Jun 04 06:07:58 ns3084948.ip-145-239-4.eu mongod[10347]: 2019-06-04T06:07:58.013+0100 I CONTROL  [main] WARNING: Cannot detect if NUMA interleaving is enabled. Failed to probe "/sys/devices...ssion denied
Jun 04 06:07:58 ns3084948.ip-145-239-4.eu mongod[10347]: about to fork child process, waiting until server is ready for connections.
Jun 04 06:07:58 ns3084948.ip-145-239-4.eu mongod[10347]: forked process: 10349
Jun 04 06:08:01 ns3084948.ip-145-239-4.eu mongod[10347]: child process started successfully, parent exiting
Jun 04 06:08:01 ns3084948.ip-145-239-4.eu systemd[1]: Started MongoDB Database Server.
Hint: Some lines were ellipsized, use -l to show in full.
[root@ns3084948 ~]#

June 4, 2019

List all files in an rpm package
To list all files in an rpm package run
```
rpm -ql PACKAGE_NAME
```
May 28, 2019

Install vsftpd on CentOS

To install vsftpd FTP server in CentOS, run

yum install -y vsftpd

Enable vsftpd to start on boot

systemctl enable vsftpd

Edit configuration file

vi /etc/vsftpd/vsftpd.conf

You need to update/add following configuration options

chroot_local_user=YES
allow_writeable_chroot=YES
local_umask=002
file_open_mode=0755
force_dot_files=YES

Restart vsftpd

systemctl restart vsftpd

Allow System Accounts to login

local_enable=YES
write_enable=YES

Find

anonymous_enable=YES

Replace With

anonymous_enable=NO

Find

#chroot_local_user=YES

Replace with

chroot_local_user=YES

Add

allow_writeable_chroot=YES
local_umask=002
file_open_mode=0755

See vsftpd

March 28, 2019

SELinux
To disable SELinux, edit
```
sed -i 's/^SELINUX=.*/SELINUX=disabled/g' /etc/selinux/config
```
Now you need to reboot. If you don’t want to reboot, disable it for current session with
```
setenforce 0
```
If you use SELinux, you may need to configure it for each applications.

For web server
```
setsebool httpd_can_network_connect true
setsebool -P httpd_can_network_connect_db 1
setsebool -P memcached_connect_any 1
```
CURL ERROR 7 could not establish a secure connection to WordPress.org
SELinux allow non default SSH port
March 17, 2019

Category: CentOS

Allow Web Access

Allow System Accounts to login