Verify if a name server is registered with
whois -h whois.verisign-grs.com "nameserver=ns20.hostonnet.com"Find all sites using a specific nameserver
To find IP of a domain, use
nslookup serverok.in
To find MX record for a domain, use
nslookup -q=mx serverok.in
To see TXT records, run
nslookup -q=txt serverok.in
When you run nslookup, it checks with caching name servers, generally provided by your ISP. But these are not authoritative name servers for your domain name. These caching name servers cache any DNS result for several hours depending on TTL (Time To Live) value in a domain’s DNS zone. If you are debugging some DNS problems, you need to ask domains authoritative name servers, that you can find by taking whois of a domain name.
Here is an example
nslookup -q=a DOMAIN_NAME_HEARE AUTHORITATIVE_NAME_SERVER_HERE
If you take whois of serverok.in, you will see the domain use name servers
Name Server: elle.ns.cloudflare.com Name Server: carl.ns.cloudflare.com
To find MX record of the domain, you can use
nslookup -q=mx serverok.in
But what you get is the cached result from a non-authoritative name server. To get an authoritative result, you need to use the following command
nslookup -q=mx serverok.in elle.ns.cloudflare.com
Here elle.ns.cloudflare.com is one of the name servers used by serverok.in, that you find from whois. You can use any of the name servers with the nslookup command.
What it does is, ask the name server elle.ns.cloudflare.com (authoritative name server) what is the MX record for the domain serverok.in
Install nslookup on ArchLinux
Find Reverse-DNS/PTR using dig, nslookup, host
How to verify rDNS (reverse DNS)/PTR Record
To start a program using cronjob, create a cronjob like
@reboot /root/start.sh
On system boot, the command “/root/start.sh” will be executed.
To install memcached on CentOS 7, run
yum -y install memcachedSet memcached to start on boot
systemctl enable memcachedStart memcached with
systemctl start memcachedInstalling PHP Module
You need remi repository installed, which provide a memcached module for all versions of php they support.
For PHP 5.6, run
yum install php-memcacheNow phpinfo() will show
See memcached
First find the Trash related settings with gsettings command.
boby@ok-pc-01:~$ gsettings list-recursively | grep -i trash org.gnome.gedit.plugins.filebrowser.nautilus confirm-trash true org.gnome.desktop.privacy remove-old-trash-files false org.gnome.eog.ui disable-trash-confirmation false org.gnome.nautilus.preferences confirm-trash true org.gnome.nautilus.preferences show-move-to-trash-shortcut-changed-dialog true org.gnome.DejaDup exclude-list ['$TRASH', '$DOWNLOAD'] org.gnome.nautilus.desktop trash-icon-name 'Trash' org.gnome.nautilus.desktop trash-icon-visible true boby@ok-pc-01:~$
To disable the Trash Icon on desktop, run
gsettings set org.gnome.nautilus.desktop trash-icon-visible false
Method 2
If you have gnome tweaks tool installed, go to Desktop, you have option to disable Trash Icon.
See Ubuntu 18.04
CentOS 7 Grub 2
grubby
OVH CentOS 7 server grub rescue prompt
Regenerate grub config
grub2-mkconfig -o /boot/grub2/grub.cfg grub2-mkconfig -o /boot/efi/EFI/centos/grub.cfg grub2-mkconfig -o /boot/efi/EFI/almalinux/grub.cfg
grub config on RHEL
/etc/default/grub
To install Grub, run
/sbin/grub2-install /dev/sda
To see all available kernels
awk -F\' '$1=="menuentry " {print i++ " = "$2}' /etc/grub2.cfg
If all kernels not showing, edit
vi /etc/default/grub
Add
GRUB_DISABLE_SUBMENU=true GRUB_DEFAULT=saved
Rebuild grub
grub2-mkconfig -o /etc/grub2.cfg
To set default Kernel
grub2-set-default 0
To see the current Kernel
grub2-editenv list
Reinstall kernel and set it to default
yum reinstall kernel grub2-set-default 0 grubby --set-default 0
sudo update-grub /usr/sbin/grub-mkconfig -o /boot/grub/grub.cfg
To handle SSL/HTTPS traffic on haproxy, use following config in your /etc/haproxy/haproxy.cfg file.
frontend https-frontend-new bind :::443 ssl crt domain.pem acl https ssl_fc http-request set-header X-Forwarded-Proto http if !https http-request set-header X-Forwarded-Proto https if https option forwardfor acl secured_cookie res.hdr(Set-Cookie),lower -m sub secure http-response replace-header Set-Cookie (.*) \1;\ secure if https !secured_cookie default_backend https-backend-new backend https-backend-new balance static-rr option httpchk cookie SRV insert indirect nocache maxidle 30m maxlife 8h server web1 BACKEND_SERVER_IP:443 check ssl verify none
domain.pem
SSL certificate of your domain in PEM format. This is done by using combining your SSL cert, private key and ca bundle.
cat yourdomain.crt yourdomain.key yourdomain.ca-bundle > yourdomain.pem
If you have more sites with SSL, you can specify SSl certs like
bind :::443 ssl crt domain.pem crt domain-2.pem crt domain-3.pem
BACKEND_SERVER_IP
This is IP of your back end server.
Restart Haproxy with
systemctl restart haproxy
To check if a systemctl service is enabled, run
systemctl is-enabled SERVICE_NAMEExample
[root@mail ~]# systemctl is-enabled memcached
disabled
[root@mail ~]#You can enable the service, so it run at boot with command
[root@mail ~]# systemctl enable memcached
Created symlink from /etc/systemd/system/multi-user.target.wants/memcached.service to /usr/lib/systemd/system/memcached.service.
[root@mail ~]# To check if a service is enabled to start on boot, run
systemctl list-unit-files | grep SERVICE_NAME_HEREExample
[root@ok ~]# systemctl list-unit-files | grep httpd
httpd.service enabled
[root@ok ~]# To auto start pm2 on boot, run
pm2 startup
This will generate auto start script for your system.
Once you started all applications, you can save it with
pm2 save
To uninstall, run
pm2 unstartup systemd
First login as the user, then start the application using pm2.
pm2 start app.js
Now save it.
pm2 save
Generate command for auto startup
pm2 startup
It will show a command. That you need to run as user root. If you have sudo privilage, you can run it with sudo as same user.
This will create a service with name pm2-USERNAME.
After reboot, you will be able to check status with command
systemctl status pm2-USERNAME
See pm2
.database
Show location of the database file.
sqlite> .database
main: /root/config.db
sqlite>
.tables
List tables in a database
sqlite> .tables
tree
sqlite>
select
To see data from table, use select statement like you do in MySQL.
select * from TABLE_NAME;
.schema
To see how a table is created, use
.schema TABLE_NAME
This is equivalent to “show create table TABLE_NAME;” command in MySQL.
When i connect to an FTP server, i get following error
root@hestia-lnx:~# lftp -u sokftp 54.37.215.1 Password: lftp [email protected]:~> dir ls: Fatal error: Certificate verification: Not trusted lftp [email protected]:~> ls -la ls: ls -la: Fatal error: Certificate verification: Not trusted lftp [email protected]:~>
To fix this, run
set ssl:verify-certificate no
You can add this to /etc/lftp.conf to make this permanant
vi /etc/lftp.conf
Add
set ssl:verify-certificate no
See lftp
When i connect to remote server using SSH using private key, it ask for passphrase every time.
root@admin:~# ssh [email protected] Enter passphrase for key '/root/.ssh/id_rsa': root@admin:~#
I want it only ask once, then remember it.
To do this, you need to run
eval `ssh-agent -s` ssh-add
When you run “ssh-add” command, it ask for your passphrase. Now you will be able to use your SSH Key with out getting promoted for passphrase.
See ssh