Using Odroid as IP Router

I purchased an Odroid-XU4 for ca. 80 EUR including power-supply and case from Pollin. The original manufacturer is hardkernel. I intended to use this small ARM computer as a router and firewall. In the past I had used routers from multiple vendors, e.g., Linksys/Cisco, TP-Link, AVM/FritzBox, Netgear, and so on. There is a rule of thumb with all these devices: Usually you have to reboot them once or twice a month, otherwise they misbehave somehow. At least three of these device went completely catatonic. Now I had enough of this, I also wanted a command line interface to the router, ideally a real Linux system with bash, cron, gcc, etc. Although I already own an Intel NUC and I am very happy with this computer, an Intel NUC is a little bit too expensive to be used as just a router.

I recommend to additionally purchase a RTC backup battery. The Odroid has a realtime clock, but looses all date and time information once powered off. This way the log of the computer is garbled.

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Wiping Disks

How fast can you wipe a complete disk? For this I dumped zeros to a MS Windows partition based on an SSD formatted with NTFS.

[root@i7 ~]# time dd if=/dev/zero of=/dev/sda1 bs=1M
dd: error writing '/dev/sda1': No space left on device
81920+0 records in
81919+0 records out
85898297344 bytes (86 GB, 80 GiB) copied, 182.699 s, 470 MB/s

real    3m2.703s
user    0m0.033s
sys     0m43.470s

It was a real pleasure to get rid of MS Windows after just 3 minutes 😉

Once more, second partition on SSD formatted with NTFS.

[root@i7 ~]# time dd if=/dev/zero of=/dev/sda2 bs=1M
dd: error writing '/dev/sda2': No space left on device
147015+0 records in
147014+0 records out
154155352064 bytes (154 GB, 144 GiB) copied, 326.108 s, 473 MB/s

real    5m26.110s
user    0m0.097s
sys     1m21.503s

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Make USB Stick Bootable

In various forums one reads that one should use dd to copy a ISO image to an USB stick. Although this works, more often you do not want to use a ISO image but rather copy a Linux system at hand. First you mount the root filesystem of the new USB stick, then mount /boot within a chroot. Finally use grub commands. I.e., type

mount /dev/sdc2 /mnt/stick
arch-chroot /mnt/stick
mount /dev/sdc1 /boot           <--- /boot is local to chroot!
grub-install --target=i386-pc --boot-directory=/boot /dev/sdc
grub-mkconfig -o /boot/grub/grub.cfg
umount /boot                    <--- umount "local" /boot

Also see GRUB in the Arch Wiki.

Setting the bootable flag in the partition table one either uses gparted, a graphical tool, or, as the task at hand is so simple, one just uses parted.

parted /dev/sdc
set 1 boot on
print

Unrelated, but often useful. Just in case you changed something in the initial RAM disk, use

mkinitcpio -p linux

Switching from ext4 to btrfs

Hearing all these wonder stories about btrfs I decided to give btrfs a try. Additionally I encrypted my SSD using LUKS.

The relevant entries in the Arch WIKI are: Setting up LUKS and btrfs. Here is the list of commands I used.

1. I saved my data from SSD using tar and saved tar-file on hard-disk:

cd /
time tar cf /mnt/c/home/klm/ssd1.tar bin boot etc home opt root srv usr var

Alternatively one can use cp -a to copy directories with symbolic links. Option -a is the same as -dR --preserve=all.

2. I used gparted to partition the SSD, creating /boot and / (root). For /boot I directly enabled btrfs in gparted.

3. Encrypt the partition.

cryptsetup -y -v -s 512 luksFormat /dev/sdc2

Then open it and give it an arbitrary name:

cryptsetup luksOpen /dev/sdc2 cryptssd

4. Create filesystem using btrfs. This is the reason for all this effort. Although this is the easiest.

mkfs.btrfs /dev/mapper/cryptssd

5. Adapt /etc/fstab, e.g., with genfstab -U /mnt >> /mnt/etc/fstab

UUID=3b8bb70c-390a-4a9e-9245-ea19af509282       /       btrfs   rw,relatime     0 0
UUID=a8d6c185-0769-4ec5-9088-2c7087815346       /boot   ext4    rw,data=ordered,relatime        0 2

Check results with lsblk -if.

6. Chroot into new system using arch-chroot and put GRUB on it, as usual. Add required directories, first.

mkdir boot proc run sys tmp

Then edit the configuraton file for GRUB:

vi /etc/default/grub
GRUB_CMDLINE_LINUX_DEFAULT="cryptdevice=UUID=5a74247e-75e8-4c05-89a7-66454f96f974:cryptssd:allow-discards root=/dev/mapper/cryptssd"

grub-install --target=i386-pc /dev/sdb
grub-mkconfig -o /boot/grub/grub.cfg

Keyword :allow-discards after cryptssd is for SSD TRIM. For a mechanical hard drive this keyword should be omitted.

7. Install btrfs utilities and programs on new system if not already installed. Add the btrfs executable to the initial RAM disk, i.e., set the entry for BINARIES.

pacman -S btrfs-progs

vi /etc/mkinitcpio.conf
. . .
BINARIES="/usr/bin/btrfs"
. . .
mkinitcpio -p linux

8. Extracting back from the tar-file.

time tar xf /mnt/c/home/klm/ssd1.tar

9. Adding TRIM for SSD:

systemctl status fstrim
systemctl enable fstrim.timer
systemctl start fstrim.timer

Show timers (like crontab -l):

systemctl --type=timer

10. A simple benchmark, as indicated by above time before tar, does not show any performance benefits so far. But performance was not the main motivator, but rather the added functionality, especially taking snapshots.

Downgrading PulseAudio with downgrade.sh

Just upgraded PulseAudio from 9.0-1 => 10.0-2, which was no good, as I was left with no sound.

The bash script downgrade.sh given in Github saved the day. Sound is back. The script is for Arch Linux.

Usage:

downgrade.sh libpulse pulseaudio pulseaudio-bluetooth

From now on I have to use

pacman -Syu --ignore pulseaudio --ignore libpulse --ignore pulseaudio-bluetooth

to not lose the good version and getting the infected version again.

slurmd confused of pid-file

I wrote on SLURM used on Ubuntu here. As I moved to Arch Linux I of course use the fine AUR package slurm-llnl maintained by Gordian Edenhofer.

After upgrading to version 16.05.7-1 I noticed the following: If slurmd is started by systemd then the pid-file specified for systemd in /lib/systemd/system/slurmd.service (PIDFile) should match the pid-file location (SlurmdPidFile) given in /etc/slurm-llnl/slurm.conf.

By the way, if one gets an error

slurm_receive_msg: Zero Bytes were transmitted or received

check your date and time of your nodes.