How To Reduce the Size of a PDF Using Ghostscript

Author: , February 4th, 2017

Make sure you have Ghostscript installed, then: 1 gs -dNOPAUSE -dBATCH -sDEVICE=pdfwrite -dCompatibilityLevel=1.4 -dPDFSETTINGS="/ebook" -sOutputFile=output.pdf input.pdf gs -dNOPAUSE -dBATCH -sDEVICE=pdfwrite -dCompatibilityLevel=1.4 -dPDFSETTINGS=”/ebook” -sOutputFile=output.pdf input.pdf -dPDFSETTINGS={value} where {value} is one of: /screen – the lowest resolution and lowest file size, fine for viewing on a screen /ebook – mid-range resolution and file size /printer – high-quality […]

How To Enable Legacy Key Type Support in SSH 7

Author: , December 9th, 2016

Recently I had to launch an Ubuntu instance in AWS because i needed to run alien to convert a .rpm into a .deb package. When I added my SSH keys as usual, I found I was still unable to login. This is the error from the /var/log/auth.log file: Dec 9 16:47:55 localhost sshd[1550]: userauth_pubkey: key […]

How To Block an Entire TLD in Postfix

Author: , September 13th, 2016

Step 1. Execute the following two commands: postconf -e smtpd_sender_restrictions=pcre:/etc/postfix/rejected_domains postconf -e reject_unauth_destinations=pcre:/etc/postfix/rejected_domains If that doesn’t work, you may hand-edit main.cf and add/edit these lines: 1 2 smtpd_sender_restrictions=pcre:/etc/postfix/rejected_domains reject_unauth_destinations=pcre:/etc/postfix/rejected_domains smtpd_sender_restrictions=pcre:/etc/postfix/rejected_domains reject_unauth_destinations=pcre:/etc/postfix/rejected_domains Step 2. Create the regex filter file: vim /etc/postfix/rejected_domains 1 2 /\.top$/           REJECT No spam allowed from the .top […]

How To Install and Use the screen Command on AWS Linux

Author: , August 12th, 2016

Install it: yum install screen Start it up: screen Detach from the session: Control-a d Re-attach to the session later on: screen -r This is a good reference guide: https://www.rackaid.com/blog/linux-screen-tutorial-and-how-to/

How To Fix Apache VirtualHost Overlap on Port 443 on AWS Linux

Author: , July 4th, 2016

If you get this error when starting Apache or via `apachectl configtest`: [warn] _default_ VirtualHost overlap on port 443, the first has precedence then you must add: NameVirtualHost *:443 to /etc/httpd/conf/httpd.conf, then restart Apache

How To Fix “No Public Key Available” Errors for apt-get update on Debian

Author: , June 29th, 2016

root@myHost # apt-get update Hit http://cloudfront.debian.net wheezy Release.gpg Hit http://cloudfront.debian.net wheezy-updates Release.gpg Hit http://cloudfront.debian.net wheezy-backports Release.gpg Hit http://cloudfront.debian.net wheezy Release Hit http://cloudfront.debian.net wheezy-updates Release Hit http://cloudfront.debian.net wheezy-backports Release Hit http://cloudfront.debian.net wheezy/main Sources Hit http://cloudfront.debian.net wheezy/main amd64 Packages Hit http://cloudfront.debian.net wheezy/main Translation-en Hit http://cloudfront.debian.net wheezy-updates/main Sources Hit http://security.debian.org wheezy/updates Release.gpg Get:1 http://cloudfront.debian.net wheezy-updates/main amd64 Packages/DiffIndex [2,488 […]

How To Fix a “Corrupted index cache file” Error in Dovecot

Author: , June 17th, 2016

Jun 17 00:02:45 inbound dovecot: IMAP(yourName): Corrupted index cache file /home/yourName/Maildir/dovecot.index.cache: invalid record size service dovecot stop cd /home/yourName/Maildir/ rm dovecot.index* service dovecot start As always, YMMV. Proceed with caution.

How To Create a PDF from Multiple Image Files on the Command Line

Author: , June 6th, 2016

convert myFile*.jpg myFile.pdf convert myFile*.png myFile.pdf

How To See a Process Tree Using the ps Command

Author: , December 16th, 2015

ps -afxt

How To Patch the Linux Ghost gethostbyname Buffer Overflow Vulnerability in glibc

Author: , January 28th, 2015

As per ARS Technica: “An extremely critical vulnerability affecting most Linux distributions gives attackers the ability to execute malicious code on servers used to deliver e-mail, host webpages, and carry out other vital functions.” To patch, run: yum update glibc Article: http://arstechnica.com/security/2015/01/highly-critical-ghost-allowing-code-execution-affects-most-linux-systems/ Amazon Alert: https://alas.aws.amazon.com/ALAS-2015-473.html Original Advisory: http://www.openwall.com/lists/oss-security/2015/01/27/9