“dd” shows its progress

Problem: “dd” is a useful tool on linux. E.g. you can copy a disk image or wipe a disk, etc. But dd doesn’t show you any progress indicator, and you don’t know how long you have to wait until it has finished.

Solution:   send signal USR1 to the dd process and it will show you how much data it has already transferred at what speed

# dd if=/dev/zero of=/dev/sdc
other terminal # killall -USR1 dd
53768289+0 records in
53768289+0 records out
27529363968 bytes (28 GB) copied, 5025.8 s, 5.5 MB/s

Howto generate an SSL key and self signed cert with openssl

For SSH, HTTPS, TLS SMTP,POPS, IMAPS you need a RSA key pair. Most Linux package installers produce this pairs automatically, but if you like, you can generate them yourself.

The quickest method I found is:

openssl req -x509 -nodes -newkey rsa:2048 -keyout servername.key -out servername.crt -days 1024

This command asks you some questions. The most important one is:

Common Name (e.g. server FQDN or YOUR name)

Enter the hostname of your server here.

You can check the content of key and crt files with these commands:

openssl rsa -in servername.key -text
openssl x509 -in servername.crt -text

Unix/Linux date command fails when calculating “yesterday”

Problem: A shell-script running every day short after midnight doesn’t work properly once per year after daylight-saving time adjustment. e.g. an expected logfile is missing (“somefile.YYYYMMDD.log”)

Discussion: The Unix date command calculates the wrong date when used with “–date yesterday” on the day after daylight-saving time adjustment.

# date
Mon Mar 31 00:15:03 CEST 2014
# date --date 'yesterday'
Sat Mar 29 23:15:09 CET 2014

Date obviously uses “24 hours ago” for yesterday. The DST adjustment day has only 23 hours, so “yesterday” is calculated wrong, between 0:00 and 1:00 on these days.

It’s interessting that “yesterday” is not allways equal to “24 hours ago”:

# date --date "2014-03-31 0:15 yesterday"
Sun Mar 30 00:15:00 CET 2014
# date --date "2014-03-31 0:15 24 hours ago"
Sat Mar 29 23:15:00 CET 2014

 

Solution: I changed the “yesterday” date calculation for nightly jobs after midnight to:

# date --date "12:00 yesterday" +%Y%m%d