How to use a proxy for common applications

Global environment
Set the HTTP_PROXY environment variable

export HTTP_PROXY=http://username:password@proxy.server:port/  

apt
Create the file /etc/apt/apt.conf.d/43proxy and place the line below (be sure to provide the appropriate proxy information):

Acquire::http::Proxy "http://username:password@proxy.server:port/";

wget
Set the proxy settings in /etc/wgetrc

http_proxy=http://server_ip:port

git
Use the command below:

git config --global http.proxy http://username:password@proxy.server:port/

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SSH without user-known hosts checking

If the IP address of the host you are connecting to frequently changes, as in the case of cloud instances, but you are sure that that you are connecting to the correct host, you can use the following ssh command to disable known host checking (Note: This may lead to MITM attacks).

ssh -o UserKnownHostsFile=/dev/null user@10.0.3.x 

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A formula for computing your hourly rate as a consultant

Let S be your regular monthly salary and your work is forty hours per week, then your hourly rate HR can be computed as:

   HR = 2.5 x (S / 160)

For example, if your salary is 12,000.00 PhP, your hourly rate is

   HR = 2.5 x (14,000.00 / 160)
      = 218.75 PhP

Now, let's say you have a website development project that you estimate will take one month (at 160 hours per month), you can charge your client 35,000.00 PhP.

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OpenLDAP+Apache

I decided to create an OpenLDAP server[1] for my research group to serve as the central storage for member information (POSIX generic account). This server will be used to authenticate users when they access certain services that should be available to group members only. The group's wiki seems like a good candidate to test the setup.
First, enable LDAP related apache modules.

sudo a2enmod ldap authnz-ldap

Next, edit /etc/apache2/apache2.conf to add the following:

<directory>
        AuthType Basic
        AuthName "This site is for SRG members only. Please use your SRG NetId credentials to access this site."
        AuthBasicProvider ldap
        #AuthzLDAPAuthoritative on
        AuthLDAPURL "ldap://[your ldap server ip addess]:389/dc=srg,dc=ics,dc=uplb,dc=edu,dc=ph?uid"
        AuthLDAPBindDN "cn=admin,dc=srg,dc=ics,dc=uplb,dc=edu,dc=ph"
        AuthLDAPBindPassword [your admin password]
        Require valid-user
</directory>

Finally, restart apache.

sudo service restart apache2

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Remove unused kernel images/headers in Ubuntu

The command below removes the image and associated headers of the kernel not currently running. This allows us to reclaim disk space in /boot (especially when created as a separate partition). The kernel version currently running (usually the latest) can be viewed using the command uname -r.

To be sure, upgrade the system first.

sudo apt-get -y update
sudo apt-get -y upgrade
sudo reboot
uname -r

Then remove the old kernel images and headers.

echo $(dpkg --list | grep linux-image | awk '{ print $2 }' | sort | sed -n '/'`uname -r`'/q;p') $(dpkg --list | grep linux-headers | awk '{ print $2 }' | sort -n | sed -n '/'"$(uname -r | sed "s/\([0-9.-]*\)-\([^0-9]\+\)/\1/")"'/q;p') | xargs sudo apt-get -y purge

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Resize images from the command line in Ubuntu

If you need to resize a lot of images to conserve disk space, you can use imagemagick. Note: mogrify will overwrite the original files.

sudo apt-get install imagemagick
mogrify -resize 1024x768 *JPG

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