Category: Linux

Allow SSH root login
To allow SSH login as user root, edit file
```
vi /etc/ssh/sshd_config
```
Find
```
PermitRootLogin no
```
Replace with
```
PermitRootLogin yes
```
restart sshd.
```
systemctl restart sshd
```
July 23, 2019

Adding a group in Linux with addgroup

addgroup linux commanhd allow you to create a group.

addgroup [options] [--gid ID] group

Example

root@ok:~# addgroup sokadmin
Adding group `sokadmin' (GID 1004) ...
Done.
root@ok:~#

Add a system group (normally group id below 500, run

addgroup --system [options] [--gid ID] group

July 23, 2019

PCI COMPLIANCE SSH Diffie-Hellman Modulus

When doing PCI COMPLIANCE scan got error related to SSH Diffie-Hellman Modulus <= 1024 Bits (Logjam). SSH Diffie-Hellman Modulus error

To fix the error, run

cp /etc/ssh/moduli /etc/ssh/moduli.backup
awk '$5 > 2000' /etc/ssh/moduli > /etc/ssh/moduli

Edit file

vi /etc/ssh/sshd_config

Add at end of the file

KexAlgorithms ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,diffie-hellman-group14-sha1,diffie-hellman-group-exchange-sha1,diffie-hellman-group-exchange-sha256

Restart sshd

systemctl restart sshd

July 21, 2019

locate command on Linux
locate command find files on a linux server.

To install locate, run

On CentOS
```
yum install mlocate
```
On Debian/Ubuntu
```
apt install mlocate
```
locate searches through a static index of files. This is rebuild daily using cronjob. You can manually update it by running
```
updatedb
```
July 21, 2019
ack better grep for programmers
ack is a tool like grep optimized for programmers.

ack show the matched files name only

On Debian/Ubuntu, you can install it with apt
```
apt install ack
```
To install from source, run
```
curl https://beyondgrep.com/ack-v3.0.2 > /usr/local/bin/ack && chmod 0755 /usr/local/bin/ack
```
For installing for just one user, run
```
curl https://beyondgrep.com/ack-v3.0.2 > ~/bin/ack && chmod 0755 ~/bin/ack
```
On RHEL/CentOS, you may need to install dependency
```
yum install perl-version
```
For the latest version, always check

https://beyondgrep.com/install/

See grep
July 21, 2019
log
Logging Linux Commands for all users
Monitor Apache site traffic with Apachetop
Find IP with Most Access from Apache Log
Apache LogFormat show full domain name
Display real time statistics with Logtop
Cpanel find recently logged in users
How to get list of User-Agent from access log

Find the most requested pages
```
awk '{print $7}' access_log.log | sort | uniq -c | sort -nr
awk '{print $7}' access_log.log | sort | uniq -c | sort -nr | head -n 10
```
To view the most used User Agents
```
cat access_log.log |   awk -F\" '{print $6}' | sort | uniq -c | sort -nr | head -n 10
```
July 20, 2019
Monitor Apache site traffic with Apachetop
apachetop is a command line tool like top, that shows traffic on a web site. It used apache access log to show th stats. This will be useful to monitor a web sites traffic in real time.
```
cd /usr/local/src
wget https://github.com/HostOnNet/apachetop/archive/master.zip
unzip master.zip
cd apachetop-master
./configure --with-logfile=/var/log/httpd/access_log
make
make install
```
If you need to set path to apache log file, configure with
```
./configure --with-logfile=/path/to/apache/log/file.log
```
On CentOS
```
yum install apachetop
```
On Ubuntu/Debian
```
apt install apachetop
```
Running apachetop with custom log file location
```
apachetop -f /path/to/apache/log/file.log
```
July 20, 2019
imunify360
Imunify360 is paid version of Imunify. It provides additional protection like Web Application Firewall, Real-time protection, and automated malware cleaning.
Update license
```
REG_KEY=XXXXX imunify360-agent register
```
If you have IP based license, use
```
imunify360-agent register
```
July 20, 2019
Resize a linux file system with resize2fs
On cloud servers, once you upgrade disk, you will need to resize the filesystem. On Linux ext4 file system, you can do this with command resize2fs.

To resize filesystem on /dev/sdb, run
```
root@leonestage:~# resize2fs /dev/sdb
resize2fs 1.44.1 (24-Mar-2018)
Filesystem at /dev/sdb is mounted on /mnt/HC_Volume_2899894; on-line resizing required
old_desc_blocks = 2, new_desc_blocks = 3
The filesystem on /dev/sdb is now 10485760 (4k) blocks long.

root@leonestage:~#
```
Here the full disk is used as file system with NO partition. If you have partion, you need to specify partition number like /dev/sdb1
July 19, 2019
Bandwidth Limit on rsync
I wanted to transfer some files between two computers, but don’t want to use all bandwidth available on the network as it will affect other users on the network.

To limit bandwidth, use –bwlimit Option.
```
rsync -avzP  --bwlimit=1500 /mnt/data/learn/css/BootStrap3/ [email protected]:/home/php-tutorial/BootStrap3/
```
Here –bwlimit=1500 will limit bandwidth usage to 1.5 MB/s.

See rsync
July 19, 2019
Install x11vnc on Ubuntu
To install x11vnc on Debian/Ubuntu, run
```
apt install -y x11vnc
```
To start vnc server, run
```
x11vnc -display :0
```
By default, there will be no password. To set password, run
```
x11vnc -storepasswd
```
To start x11vnc server with password, run
```
x11vnc -rfbauth ~/.vnc/passwd
```
July 17, 2019
Upload all files to FTP server using lftp
lftp allow you to upload all files and sub folders using single command. With normal ftp command, you need to use put/mput command many times to do the same.

To download all files from FTP server, use “mirror” command. mirror command also allow you to upload files to remote server by specifying -R (reverse mirror) option.

This is very useful for uploading files from SSH shell account.

For help, use ? in lftp command prompt. To get help for specific command use
```
help 
```
Exampe
```
help mirror
```
To upload all files from local folder to remote server, run
```
lftp -d -u FTP_USER,FTP_PASSWORD FTP_SERVER_IP
set ftp:ssl-allow no
mirror -R /var/flashwebhost/vshare2.7/ public_html
```
Following will upload vshare2.7 folder to FTP root folder.
```
unzip vshare2.7.zip
lftp -d -u FTP_USER FTP_SERVER_IP
set ftp:ssl-allow no
mirror -R vshare2.7
```
See lftp
July 17, 2019

Category: Linux

On CentOS

On Ubuntu/Debian

Running apachetop with custom log file location