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
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
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.
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
When you have a mysql table with lot’s of attributes, it’s hard to read the output of a statement like this in mysql:
select * from table limit 1;
The data is folded very ugly.
select * from table limit 1 \G
Mysql is showing one “Fieldname: Value” per line.