Howto fix a too sensitive touchpad on Linux

If your touchpad is too sensitive (meaning the cursor jumps around when you either put your finger on the touchpad or you remove your finger from the touchpad) then here’s how to fix it:

Open a terminal window and find out the ID of the touchpad:

The output should look something like this:

So the touchpad (an Alps in my case) has ID 13.

Now let’s list the properties (settings) of the touchpad:

The output should look something like this:

The setting to look for is “Synaptics Finger”:

The “298” is the ID of the setting and the “12, 15, 0” values represent FingerLow, FingerHigh and FingerPress. You can read about their meaning here

Start increasing the first 2 values each in increments of 2 with the following command. The changes become active immediately. If the touchpad is still too sensitive then keep on increasing those values until the problem is solved.

The syntax of the command is:

In my case the values that solved the problem were:

Once the proper values are found they can be made permanent by adding them to the InputClass of the synaptics config file:

If the problem can not be solved by changing the FingerLow and FingerHigh values then there are a ton of links in Google that discuss this problem. An excellent resource is https://wiki.archlinux.org/index.php/Touchpad_Synaptics

How to replace a failed disk with Linux software RAID (mdadm)

Recently one of the disks died in a RAID1 setup which uses the excellent Linux software RAID (mdadm). Here is a quick overview of the steps to exchange the failed disk with a new one. Obviously you should replace the X in /dev/mdX with the proper number of your RAID device. The same applies to /dev/sddY. Replace it with the actual device and partition you are using. So don’t copy and paste these commands. All commands should be executed as root or with proper sudo rights.

Step 1 – mark broken disk as failed

Step 2 – remove broken disk from array

Step 3 – create partition on the new disk

You can partition the new disk manually using your favourite tool (fdisk, gparted, sfdisk, etc.). But it’s probably faster and less error prone to copy the partition from an existing RAID disk to the new disk. Here’s an example how to do that using sfdisk. Requirement: the disk must be smaller than 2TB and should not be using GPT.

Make sure that all the partitions that are part of the RAID set have the proper ‘fd’ ID (Linux RAID autodetect). And example to set the ID of partition 1, 2 and 3 on the new disk to ‘fd’:

Step 4 – add new disk to RAID array

Step 5 – check status of RAID array

Step 6 – increase speed of the rebuild

By default mdadm will rebuild the RAID array in the background. If you want to speed up the resync process you can change the values of:

/proc/sys/dev/raid/speed_limit_max
/proc/sys/dev/raid/speed_limit_min

For example to set the minimum resync speed to 150MB/s:

You can watch the progress of the resync in a terminal with the following command:

Finally, for your next RAID setup also have a look at Partitionable RAID.

How to reduce in size, shrink, optimize a pdf

For administrative purposes I scan all important paper documents to pdf. Sometimes those pdf files are quite big. Here are a few ways you can reduce in size, shrink and optimize a pdf.

Use pdf2ps and ps2pdf

The simplest way is to use the pdf2ps and ps2pdf (ps2pdf14) commands. They are part of the Ghostscript package so make sure you have ghostscript installed:

Next let’s see the results when using this on a 11MB pdf file called big.pdf

So the size went down from 11MB to 9,1MB. That’s not a very big improvement. As you can imagine results vary. At times these default commands can significantly reduce the size and sometimes not. If not, there are more tricks.

Use ps2pdf with options

If the reduction in size is not enough then it’s time to look at some of the ps2pdf options. man ps2pdf has a very long list of options with which you can experiment. The option that has a significant impact on the size of a pdf is -dPDFSETTINGS=…

The PDFSETTINGS option can be set to:

  1. /screen – for low-resolution output similar to the Acrobat Distiller “Screen Optimized” setting
  2. /ebook for medium-resolution output similar to the Acrobat Distiller “eBook” setting
  3. /printer for output similar to the Acrobat Distiller “Print Optimized” setting
  4. /prepress for output similar to Acrobat Distiller “Prepress Optimized” setting
  5. /default for a wide variety of uses, possibly at the expense of a larger output file

For a long list of ps2pdf options check out the ps2pdf page

Let’s try the /ebook option and see what the results are:

The size of the pdf went down from 11M to below 2M.

Other ways

Ghostscript (gs) is the de facto pdf read/write engine in the Linux world. So all other ways to process a pdf file are basically using that.

Shrinkpdf
Shrinkpdf (available here) is a nice script to process pdf files with pre-determined settings.

The Ghostscript gs command
You can also directly use the Ghostscript gs command which pfd2ps, ps2pdf and shrinkpdf use. For example to convert a postscript (ps) file to a pdf with Ghostscript’s gs command: