Category: Linux

  • self signed ssl

    To generate self signed SSL certificate, run

    openssl genrsa -out DOMAIN_NAME_HERE.key 2048
openssl req -new -x509 -key DOMAIN_NAME_HERE.key -out DOMAIN_NAME_HERE.crt -days 3650 -subj /CN=DOMAIN_NAME_HERE

    Or

    openssl req -newkey rsa:2048 -nodes -keyout DOMAIN_NAME_HERE.key -x509 -days 3650 -out DOMAIN_NAME_HERE.crt

    Add Self Signed SSL to Apache Virtual Host

    Let’s say your Apache virtual host entry is

    <VirtualHost *:80>
    ServerName serverok.in
    ServerAlias www.serverok.in
    ServerAdmin [email protected]
    DocumentRoot /home/serverok.in/public_html
    <Directory "/home/serverok.in/public_html">
        Options All
        AllowOverride All
        Require all granted
        Order allow,deny
        allow from all
    </Directory>
</VirtualHost>

    Create a new VirtualHost entry based on this, say yourdomain-ssl.conf, in this new file

    Find

    <VirtualHost *:80>

    Replace with

    <VirtualHost *:443>

    Find line starting with

    DocumentRoot

    Add Below

    SSLEngine on
SSLCertificateFile /etc/ssl/yourdomain.crt
SSLCertificateKeyFile /etc/ssl/yourdomain.key

    Now restart Apache

    systemctl restart apache2

    How to access the website using a Self-signed SSL certificate

    See SSL

  • sublime

    sublime shortcuts

    CTRL + D = select all occurrence of a word.
CTRL + L = select current line.
SHIFT + LEFT/RIGHT ARROW = select a word.

  • bash

    Bash shortcuts

    CTRL + U = Delete everything
CTRL + W = Delete a word
CTRL + A = Go to Line starting
CTRL + E = Go to Line end 
CTRL + LEFT/RIGHT ARROW = move cursor by one word

    Enable color prompt

    Edit .bashrc, add following

    export PS1='${debian_chroot:+($debian_chroot)}\[\033[01;32m\]\u@\h\[\033[00m\]:\[\033[01;34m\]\w\[\033[00m\]\$ '

  • postfix

    Postfix Mail Server

    Postfix Configuration

    Postfix relay

    Postfix Errors

  • Configure postfix to relay mails using SendGrid

    To use postfix to send email using sendgrid, you first you need to install postfix on your server. Edit main.cf

    vi  /etc/postfix/main.cf

    Find

    relayhost =

    Delete the line. Go to end of the file and add following

    smtp_sasl_auth_enable = yes
smtp_sasl_password_maps = hash:/etc/postfix/sasl_passwd
smtp_sasl_security_options = noanonymous
smtp_sasl_tls_security_options = noanonymous
smtp_tls_security_level = encrypt
header_size_limit = 4096000
relayhost = [smtp.sendgrid.net]:587

    Create API Key in SendGrid

    Next you need to create an API key in sendgrid. To do this, go to Settings > API Key.

    https://app.sendgrid.com/settings/api_keys

    SendGrid API key

    Click “Create API Key” button.

    Sendgrid create api key

    For this test, i just give the new API key Full Access. On next page you will get API key. Copy it and keep it safe as you won’t be seeing it again.

    sendgrid api key created

    Now you have the SendGrid.com API key, that you can use with postfix.

    Add API Key to postfix

    Edit file

    vi /etc/postfix/sasl_passwd

    Add

    [smtp.sendgrid.net]:587 apikey:YOUR_API_KEY_HERE

    Here is what i have

    root@honVm:~# cat /etc/postfix/sasl_passwd
    [smtp.sendgrid.net]:587 apikey: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
    root@honVm:~#

    Now run

    postmap /etc/postfix/sasl_passwd

    To test email, run

    postsuper -d ALL
systemctl restart postfix
> /var/log/mail.log
echo "Hello" | mail -s "test" [email protected]
tail -f /var/log/mail.log

  • spam

    Incoming & Outgoing spam filer (SAS)

    Link Spam

    Captcha

    https://www.hcaptcha.com

  • fping

    fping can be used to ping multiple IP and get report.

    root@backup:~# fping -s -r 1 158.69.109.222 158.69.109.67 158.69.109.179 158.69.185.224
158.69.109.222 is alive
158.69.109.67 is alive
158.69.109.179 is alive
158.69.185.224 is alive

       4 targets
       4 alive
       0 unreachable
       0 unknown addresses

       0 timeouts (waiting for response)
       4 ICMP Echos sent
       4 ICMP Echo Replies received
       0 other ICMP received

 0.45 ms (min round trip time)
 0.54 ms (avg round trip time)
 0.62 ms (max round trip time)
        0.076 sec (elapsed real time)

root@backup:~#

    If you just want to show if hosts are up or not

    root@hon-vpn:~# fping 158.69.56.236 192.99.182.223 192.99.182.192 192.99.182.193 192.99.182.238 158.69.101.41 158.69.101.58
158.69.56.236 is alive
192.99.182.223 is alive
192.99.182.192 is alive
192.99.182.193 is alive
192.99.182.238 is alive
158.69.101.41 is alive
158.69.101.58 is alive
root@hon-vpn:~#

  • DirectAdmin CustomBuild versions.txt is getting old

    I got following email from DirectAdmin server.

    New Message: CustomBuild versions.txt is getting old on s1.serverok.in

    A new message or response with subject:

    CustomBuild versions.txt is getting old on s1.serverok.in

    has arrived for you to view.
    Follow this link to view it:

    http://s1.serverok.in:2222/CMD_TICKET?action=view&number=000000967&type=ticket

    ================================
    Automated Message Generated by DirectAdmin 1.52.1

    Do Not Reply.

    DirectAdmin is telling you to update your server.

    You need to login to SSH as user root. Then run following commands.

    cd /usr/local/directadmin/custombuild
./build update
./build all d
./build rewrite_confs

  • postfix no local interface found

    When starting postfix it failed with following error

    [root@cloud1 etc]# service postfix start
Redirecting to /bin/systemctl start postfix.service
Job for postfix.service failed because the control process exited with error code. See "systemctl status postfix.service" and "journalctl -xe" for details.
[root@cloud1 etc]# service postfix status
Redirecting to /bin/systemctl status postfix.service
● postfix.service - Postfix Mail Transport Agent
   Loaded: loaded (/usr/lib/systemd/system/postfix.service; enabled; vendor preset: disabled)
   Active: failed (Result: exit-code) since Mon 2017-12-04 09:13:07 UTC; 4s ago
  Process: 21324 ExecStart=/usr/sbin/postfix start (code=exited, status=1/FAILURE)
  Process: 21322 ExecStartPre=/usr/libexec/postfix/chroot-update (code=exited, status=0/SUCCESS)
  Process: 21319 ExecStartPre=/usr/libexec/postfix/aliasesdb (code=exited, status=75)

Dec 04 09:13:05 cloud1.serverok.in systemd[1]: Starting Postfix Mail Transport Agent...
Dec 04 09:13:05 cloud1.serverok.in aliasesdb[21319]: /usr/sbin/postconf: fatal: parameter inet_interfaces: no local interface found for ::1
Dec 04 09:13:06 cloud1.serverok.in aliasesdb[21319]: newaliases: fatal: parameter inet_interfaces: no local interface found for ::1
Dec 04 09:13:06 cloud1.serverok.in postfix[21324]: fatal: parameter inet_interfaces: no local interface found for ::1
Dec 04 09:13:07 cloud1.serverok.in systemd[1]: postfix.service: control process exited, code=exited status=1
Dec 04 09:13:07 cloud1.serverok.in systemd[1]: Failed to start Postfix Mail Transport Agent.
Dec 04 09:13:07 cloud1.serverok.in systemd[1]: Unit postfix.service entered failed state.
Dec 04 09:13:07 cloud1.serverok.in systemd[1]: postfix.service failed.
[root@cloud1 etc]#

    To fix, edit /etc/postfix/main.cf

    Find

    #inet_interfaces = all
#inet_interfaces = $myhostname
#inet_interfaces = $myhostname, localhost
inet_interfaces = localhost

    Replace with

    inet_interfaces = all

    See postfix

  • subprocess installed post-installation script returned error

    When installing software on Ubuntu, i get following error.

    It is likely that 4.5.2-armada375 belongs to a chroot's host
Building only for 4.9.58-armada375
Building initial module for 4.9.58-armada375
Error! Bad return status for module build on kernel: 4.9.58-armada375 (armv7l)
Consult /var/lib/dkms/spl/0.6.5.6/build/make.log for more information.
dpkg: error processing package spl-dkms (--configure):
 subprocess installed post-installation script returned error exit status 10
Setting up dh-python (2.20151103ubuntu1) ...
Processing triggers for libc-bin (2.23-0ubuntu3) ...
Errors were encountered while processing:
 spl-dkms
E: Sub-process /usr/bin/dpkg returned an error code (1)

    To fix this, run

    rm /var/lib/dpkg/info/PACKAGE_NAME_HERE.*
dpkg --configure -a
apt update

    Replace PACKAGE_NAME_HERE with actual package that fail. In this cause spl-dkms.

    root@ns539260:/var/lib/dpkg/info# ls -l | grep spl
-rw-r--r-- 1 root root   11811 Nov 22 07:41 spl-dkms.list
-rw-r--r-- 1 root root   19548 Apr  7  2016 spl-dkms.md5sums
-rwxr-xr-x 1 root root     891 Apr  7  2016 spl-dkms.postinst
-rwxr-xr-x 1 root root     312 Apr  7  2016 spl-dkms.prerm
root@ns539260:/var/lib/dpkg/info# rm spl-dkms.*

    See apt

  • Content Delivery Network (CDN)

  • update-alternatives

    Set default editor in Ubuntu

    To change vi editor run

    root@backup:~# update-alternatives --config vi
There are 2 choices for the alternative vi (providing /usr/bin/vi).

  Selection    Path                Priority   Status
------------------------------------------------------------
* 0            /usr/bin/vim.basic   30        auto mode
  1            /usr/bin/vim.basic   30        manual mode
  2            /usr/bin/vim.tiny    10        manual mode

Press  to keep the current choice[*], or type selection number: 
root@backup:~#

    To display current vi config, run

    root@backup:~# update-alternatives --display vi
vi - auto mode
  link best version is /usr/bin/vim.basic
  link currently points to /usr/bin/vim.basic
  link vi is /usr/bin/vi
  slave vi.1.gz is /usr/share/man/man1/vi.1.gz
  slave vi.fr.1.gz is /usr/share/man/fr/man1/vi.1.gz
  slave vi.it.1.gz is /usr/share/man/it/man1/vi.1.gz
  slave vi.ja.1.gz is /usr/share/man/ja/man1/vi.1.gz
  slave vi.pl.1.gz is /usr/share/man/pl/man1/vi.1.gz
  slave vi.ru.1.gz is /usr/share/man/ru/man1/vi.1.gz
/usr/bin/vim.basic - priority 30
  slave vi.1.gz: /usr/share/man/man1/vim.1.gz
  slave vi.fr.1.gz: /usr/share/man/fr/man1/vim.1.gz
  slave vi.it.1.gz: /usr/share/man/it/man1/vim.1.gz
  slave vi.ja.1.gz: /usr/share/man/ja/man1/vim.1.gz
  slave vi.pl.1.gz: /usr/share/man/pl/man1/vim.1.gz
  slave vi.ru.1.gz: /usr/share/man/ru/man1/vim.1.gz
/usr/bin/vim.tiny - priority 10
  slave vi.1.gz: /usr/share/man/man1/vim.1.gz
  slave vi.fr.1.gz: /usr/share/man/fr/man1/vim.1.gz
  slave vi.it.1.gz: /usr/share/man/it/man1/vim.1.gz
  slave vi.ja.1.gz: /usr/share/man/ja/man1/vim.1.gz
  slave vi.pl.1.gz: /usr/share/man/pl/man1/vim.1.gz
  slave vi.ru.1.gz: /usr/share/man/ru/man1/vim.1.gz
root@backup:~#