Remove Already Merged Branches from Git

In case you need that, here is the draft:

git branch --merged master | sed -n 's,^ \+\(.*\)$,\1,p' | xargs git branch -d

Tmate cheatsheet

If you detached tmate, you might want to re-attach by:
tmate -S /tmp/tmate-0/DpfNjI attach

iptables - deny connecting to a host

I would like to test a scenario where server A cannot reach server B. To establish this, I will add iptables rules on server A so ssh connections fail. After some research (basically reading this article) I managed to come up with the rules I need. Before doing anything it is good to know the state of the system. Use
iptables -S
to find out existing rules on your system. To block connections to ssh, use:
iptables -A OUTPUT -p tcp --dport ssh -d 192.168.124.82 -j REJECT
removing the rule is simple, list the rules with iptables -S and replace -A with -D:
iptables -D OUTPUT -d 192.168.124.82/32 -p tcp -m tcp --dport 22 -j REJECT --reject-with icmp-port-unreachable

Running Cinder Migration Unit Tests

Cinder has some unit tests for migration. If you want to run them on your computer, you'll need to set up database administrator accounts for your backends, and export an environment variable before running the test:
One-liner:

for backend in \
    mysql+pymysql://root:secret@localhost/mysql \
    postgresql://postgres:secret@localhost/cinder \
    sqlite:///somefile.db \
; do
    OS_TEST_DBAPI_ADMIN_CONNECTION=$backend \
        python -m subunit.run cinder.tests.unit.test_migrations |
            subunit2pyunit
done

MySQL

OS_TEST_DBAPI_ADMIN_CONNECTION='mysql+pymysql://root:secret@localhost/mysql'\
 python -m subunit.run cinder.tests.unit.test_migrations | subunit2pyunit

PostgreSQL

OS_TEST_DBAPI_ADMIN_CONNECTION='postgresql://postgres:secret@localhost/cinder'\
 python -m subunit.run cinder.tests.unit.test_migrations | subunit2pyunit

SQLite

OS_TEST_DBAPI_ADMIN_CONNECTION='sqlite:///somefile.db'\
 python -m subunit.run cinder.tests.unit.test_migrations | subunit2pyunit

PostgreSQL Notes

Backup a Database

sudo -u postgres --format=custom --file=<file name> <database name>

Restore a Database

First, create an empty database:

create database <database name> with encoding='utf-8';

Then grant all permissions to your user:

grant all on database <database name> to <user name>;

Then restore the dump:

sudo -u postgres pg_restore \
    --schema=public \
    --dbname=<database name> \
    --no-owner \
    --no-privileges \
    --role=<user name> \
    <file name>

System backup

• Transfer all the files to the new partition

  rsync -aAXvHS --exclude={"/dev/*","/proc/*","/sys/*","/tmp/*","/run/*","/mnt/*","/media/*","/lost+found","/data"} /* /mnt/backup/
  

• Get the UUID for the new partition

  [root@archie /]# blkid /dev/sda2 
  /dev/sda2: UUID="ca2f7146-122f-4746-8725-7aeb4ca792e6" TYPE="ext4" PARTUUID="48c724bf-02"
  

• Edit mountpoints

  [root@archie /]# vim /etc/fstab
  

• Edit the new system's boot configuration

  [root@archie /]# vim /mnt/backup/boot/syslinux/syslinux.cfg
  

• Enter the new system and fix booting

  [root@archie /]# arch-chroot /mnt/backup/
  sh-4.3# syslinux-install_update -i -a -m
  Syslinux BIOS install successful
  Boot Flag Set - /dev/sda2
  Installed MBR (/usr/lib/syslinux/bios/mbr.bin) to /dev/sda
  

Burning Blu Ray Discs

Look at this blog
For mkudffs, see arch: udftools

What I get is

24712708096/25000000000 (98.9%) @0.9x, remaining 1:08 RBU 100.0% UBU  76.6%
24726929408/25000000000 (98.9%) @0.9x, remaining 1:04 RBU 100.0% UBU  79.7%
24741150720/25000000000 (99.0%) @0.9x, remaining 1:01 RBU 100.0% UBU  85.9%
24755372032/25000000000 (99.0%) @0.9x, remaining 0:58 RBU 100.0% UBU  73.4%
:-[ WRITE@LBA=b87400h failed with SK=5h/END OF USER AREA ENCOUNTERED ON THIS TRACK]: Input/output error
:-( write failed: Input/output error
/dev/sr2: flushing cache
/dev/sr2: closing track
/dev/sr2: closing session
:-[ CLOSE SESSION failed with SK=5h/INVALID FIELD IN CDB]: Input/output error
/dev/sr2: reloading tray