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From autofs to systemd.automount

The venerable autofs mechanism to automatically mount and unmount network shares still works with today's systems but lately I noticed that NFS and CIFS shares would hang when I unplug my laptop from the local network and connect at another site (e.g. work, or a random coffee shop) where the usual network shares are not reachable. More and more processes will hang (and waiting for the network resource to re-appear) and eventually the machine will be almost unusable and only a reboot may help.

Of course one could configure a VPN to make these resources available all the time, but I don't really need these network shares and I'm already running a VPN when I'm out and about, so this would be unnecessary and overly complicated. With the reign of systemd it is now possible to have systemd handle automounting via the systemd.automount unit, so let's see if it handles these situations better.


While several tutorials on how to implement this already exist, let's recap first how autofs works. The main configuration file is /etc/auto.master, containing nothing more than:
In /etc/auto.master.d the real map files are referenced:
$ cat /etc/auto.master.d/local.autofs 
/mnt/smb /etc/auto.cifs
/mnt/nfs /etc/auto.nfs
These map files will contain the share definitions:
# auto.cifs
win0  -fstype=cifs,vers=3.0,fsc,guest,rw,nodev,nosuid,noexec,fsc ://smb/win0
win1  -fstype=cifs,vers=3.0,fsc,guest,ro,nodev,nosuid,noexec,fsc ://smb/win1

# auto.nfs
data0  -fstype=nfs,rw,nodev,nosuid,noexec,bg,intr,sec=sys,acl,fsc nfs:/mnt/data0
data1  -fstype=nfs,ro,nodev,nosuid,noexec,bg,intr,sec=sys,acl,fsc nfs:/mnt/data1
Once autofs.service is reloaded, the shares should be accessible.


But let's dismantle all that and now turn to systemd.automount. For each (network) share we will need a .mount and also a .automount unit file:
$ cat /usr/local/etc/mnt-nfs-data0.mount 
Description=NFS data0


$ cat /usr/local/etc/mnt-nfs-data0.automount 
Description=Automount NFS data0


Link both unit files to /etc/systemd/system, repeat for each network share as needed:
sudo ln -s /usr/local/etc/mnt-nfs-data0.mount     /etc/systemd/system/
sudo ln -s /usr/local/etc/mnt-nfs-data0.automount /etc/systemd/system/
The .mount unit files only need to be linked; the .automount files need to be enabled and started:
sudo systemctl enable mnt-nfs-data0.automount
sudo systemctl start  mnt-nfs-data0.automount
With that, the share should be accessible:
$ mount | grep -m1 mnt/nfs
systemd-1 on /mnt/nfs/data0 type autofs (rw,relatime,fd=48,pgrp=1,timeout=0[...]
This configuration has now been running on my laptop for a few months and it feels like it behaves better when these network resources go away and the machine isn't locking up any more. Yay \o/

conditional name resolving with dnsmasq

For some reason I needed to install a lightweight DNS forwarder on my local machine. A host file would not be sufficient, I really needed some kind of local DNS machinery that allows for specific queries to be answered by certain DNS servers. But looking more closely, there were already two DNS servers running on that machine:
$ sudo netstat -lnpu | grep :53\ 
udp*  3845/systemd-resolved
udp*  3189/dnsmasq  
The first one is systemd-resolved, that mainly seems to care about which resolv.conf to use and provides only some basic configuration parameters, not sufficient to what's needed here.

The second one is from libvirtd, running on the default address of the virtual virbr0 interface. And indeed, some parameters could be adjusted and the following actually worked:
$ sudo virsh net-edit --network default
    <forwarder domain='' addr=''>
    <forwarder domain=''  addr=''/>
    <forwarder addr=''/>

$ sudo virsh net-destroy --network default
$ sudo virsh net-start   --network default
This would forward queries for to and all queries not listed here to That was kind of what was needed, but these rules needed to be updated from time to time and editing XML stanzas for DNS entries felt somewhat unnatural. Also, with that setup I would depend on libvirt to always be installed and in working condition. If, for some reason, the libvirt setups breaks and its dnsmasq instance doesn't come up, the system would have no DNS services. But since dnsmasq was installed anyway, let's just use that.

After disabling systemd-resolved, the DNS part of libvirt's dnsmasq instance needed to be disabled too:

  <dns enable='no'/>
With that, port 53 was free to use and a new dnsmasq instance could be spawned.
$ cat /etc/dnsmasq.d/local.conf

All unspecified queries will go to We could also omit that and with the absence of a no-resolv directive, dnsmasq will forward all unspecified queries to a name server specified in /etc/resolv.conf. That way we can have distinct (private) name servers for certain domains, and a stable fallback for everything else. Neat :-)

iSCSI fun

Long time no blog post, I know. Maybe this has to do with the fact that all these posts have always been mental notes to myself first, and bits of lessons learned for the everybody else second and most of my mental notes end up in a wiki installation of mine, which gets updated way more often than this blog :-\

Anyway, the other day I was trying to build Android for a Sony phone but I didn't have enough disk space on my laptop to do so. Checking out all the sources and the build takes almost 200 GB of space - but luckily I had an (encrypted) external disk available that I could use just for this. Once plugged in and decrypted I realized that I really wanted the build environment to match the proposed requirements as closely as possible. Running a Fedora 28 desktop, let's use a Ubuntu 18.04 virtual machine for the actual build:
$ vboxmanage createhd disk --filename /opt/vm/generic/disk2.vdi --size 204800 --variant Fixed
$ vboxmanage storageattach ubuntu0 --storagectl SATA --device 0 --port 2 --type hdd --medium /opt/vm/generic/disk2.vdi
Note that we use a fixed disk image to prevent some nasty I/O errors within that virtual machine. With all that in place, we could start the machine and start to build AOSP. With regards to the aforementioned nasty I/O errors, I really must give credit to btrfs in this scenario with its built-in data checksums. I know, ZFS has this feature for ages but as this still isn't available upstream, btrfs is the next best thing.

So, while this was all fine and dandy, I still had this disk enclosure attached to my laptop and thus I couldn't move around with my laptop as I usually do. Talk about #firstworldproblems! :-) So, why not attach the enclosure to my "server" instead and see if I could somehow access the enclosure over WiFi? For some reason the first thing that pops into my head was NBD and while I had an network block device setup going in the past, it wasn't much fun and would fail too often. So let's use iSCSI instead.

Once the disk enclosure was attached to the "server", the block devices needed to be passed on to the Xen DomU that was supposed to present them as an iSCSI target:
$ lsblk /dev/sd[de]
sdd    8:48   0 931.5G  0 disk 
sde    8:64   0 931.5G  0 disk 
$ xl block-attach virt2 'format=raw, vdev=xvdd, access=rw, target=/dev/sdd'
$ xl block-attach virt2 'format=raw, vdev=xvde, access=rw, target=/dev/sde'
In the virtual machine, the tgt needed to be installed and configured:
$ cat /etc/tgt/conf.d/md0.conf 
default-driver iscsi

# RAID-0
<target iqn.example.local:virt2-sdd>
    backing-store dev/sdd
With that in place, we can go back to our laptop again and attach the disk:
$ iscsiadm -m discovery -t sendtargets -p virt2,1 iqn.example.local:virt2-sdd

$ iscsiadm -m node --targetname "iqn.example.local:virt2-sdd" --portal --login

$ lsblk /dev/sdb 
sdb    8:16   0  1.8T  0 disk
This worked :-)

Now we can decrypt the disk (sdb) again and make it available to our VirtualBox VM. It may not be the fastest setup (WiFi being the bottleneck), but it worked and now I can move around with my laptop again, with the disk enclosure sitting somewhere else. Yay! :-)

How to copy a DVD

The other day my neighbor came over and asked me if it was possible to make a copy of a DVD, and then burn the copy to a blank DVD, so that it can be played in a DVD player. I rarely use DVDs and my current computer doesn't even have a DVD drive anymore, so I used an older MacBook Pro for this task.

Looking back, the easiest way to do this would be to get a copy of the movie from DVD somewhere else and then find out how to make a playable DVD out of it, but why not go the whole way and find out about the extraction part as well?

DVD Ripping

The proper term here seems to be Ripping and in the past I sometimes used the wonderful HandBrake to do just that. Handbrake can then convert the ripped copy to other formats, but we're not quite there yet.

Usually it was sufficient to play a DVD once with VLC which would then use libdvdcss to store the CSS key in ~/.dvdcss, in turn allowing HandBrake to decrypt the same, which is essential for the rip to complete. And while this worked beforeTM, this time the resulting video was all distorted and felt like watching an old, mangled VHS tape, so something wasn't right.

The internet was full of similar reports and suggestions too, the main theme being "Just install libdvdcss to the correct location for HandBrake to find and it should just work". Well, instead of just relying on VLC to do the decryption once, I did install libdvdcss via Homebrew, hoping that Handbrake will be able to find it:

$ otool -L /usr/local/lib/libdvdcss.dylib
        /usr/local/opt/libdvdcss/lib/libdvdcss.2.dylib (compatibility version 5.0.0, current version 5.0.0)
        /System/Library/Frameworks/CoreFoundation.framework/Versions/A/CoreFoundation (compatibility version 150.0.0, current version 1259.20.0)
        /System/Library/Frameworks/IOKit.framework/Versions/A/IOKit (compatibility version 1.0.0, current version 275.0.0)
        /usr/lib/libSystem.B.dylib (compatibility version 1.0.0, current version 1226.10.1)

And lo and behold, Handbrake did find the library, but then would crash reliably when trying to open the DVD. Bummer. And only the closing comment in the same bug report shed some light on this, suggesting that 1) libdvdcss is not recommended anyway and 2) another tool named "MakeMKV" would help here.
And off we are, still trying to complete the DVD ripping part, when we could have just downloaded the movie from somewhere else :-) Luckily MakeMKV really did the trick and was easy enough to use, and offers a 30 60 day trial version, which is just fine for this one-off experiment.

DVD Creation

MakeMKV produced a ~3 GB file (MPEG-2 Video, AC3 Audio) which now needed to be converted into the DVD-Video format and finally burned onto a blank DVD-R.

I had Burn installed on this Mac, and while it is able to burn DVD-Video, it wouldn't understand the .mkv container format. The interwebs are full of recommendations for something called "iSkysoft DVD Creator", which is offered from so many shady looking websites, and under so many different alternate names that it's hard to not suspect something sinister. At least on first sight, the image does not present itself as malware, so maybe it's safe enough to try? After removing my tin foil hat and installing, this DVD creator was indeed able to parse the .mkv file and burn a DVD-Video disc in the correct format. But, as I was using the Trial Version, the whole movie was overlayed with a huge visible watermark. Lacking official documentation regarding this fact, I should have suspected for this to happen. Hm, so...what else is out there?

Digging through the Homebrew-Cask database I found DVDStyler, which should be up to the task as well. And it's released as Open Source software, cool beans!

The DVDStyler interface felt a bit awkward, but never look a gift horse in the mouth (I can't believe that this is a real proverb in the English language!) and a few mouse clicks and a coffee later, a DVD-Video copy was produced. Yay!

Next time I must remember to direct my neighbor to the next video-on-demand platform instead of ever fumbling with DVD copies again :-)


Signal Desktop on Fedora

Signal Desktop has been released some time ago and while a native application may have its advantages, it also needs time and effort until it will be available for other platforms.

Binary installation

The install routine for "Debian-based Linux" instructs us to do the following:

 > curl -s | sudo apt-key add -
 > $ echo "deb [arch=amd64] xenial main" | \
 >   sudo tee -a /etc/apt/sources.list.d/signal-xenial.list
 > $ sudo apt update && sudo apt install signal-desktop
With only a Fedora distribution around, we could of course use alien to install the package, but:

$ sudo dnf install alien
Transaction Summary
Install  70 Packages
....let's not and instead do this manually. Luckily, their download directory structure adhers to the Debian Repository Format, so with a bit of fiddling we can produce the necessary URLs:

$ curl -sLO
$ gpg --recv-keys D980A17457F6FB06

$ gpg --verify InRelease
gpg: Signature made Wed 20 Dec 2017 11:43:08 AM PST
gpg:                using RSA key D980A17457F6FB06
gpg: Good signature from "Open Whisper Systems " [unknown]
Primary key fingerprint: DBA3 6B51 81D0 C816 F630  E889 D980 A174 57F6 FB06
The InRelease is signed and contains checksums to the Packages file:

$ curl -sLO
$ sha256sum Packages 
121c0e796cef911240bb39b6d5ebed747202e9be8261808ecbf3fc4641da9e7b  Packages

$ grep 121c0e796cef911240bb39b6d5ebed747202e9be8261808ecbf3fc4641da9e7b InRelease 
121c0e796cef911240bb39b6d5ebed747202e9be8261808ecbf3fc4641da9e7b     2578 main/binary-amd64/Packages
Let's look at the Packages file for the actual packages available for download:

$ egrep '^(Package|SHA256|File|$)' Packages 
Package: signal-desktop
Filename: pool/main/s/signal-desktop/signal-desktop_1.1.0_amd64.deb
SHA256: 74ee408fa5c7047b1f2a7faa2a9fe0d5947f7f960bd7776636705af69a6b1eec

Package: signal-desktop
Filename: pool/main/s/signal-desktop/signal-desktop_1.0.41_amd64.deb
SHA256: 9cf87647e21bbe0c1b81e66f88832fe2ec7e868bf594413eb96f0bf3633a3f25

Package: signal-desktop-beta
Filename: pool/main/s/signal-desktop-beta/signal-desktop-beta_1.1.0-beta.6_amd64.deb
SHA256: a38eb35001618019affba7df4e54ccbb36581d232876e0f1af9622970b38aa12
We decide to use the signal-desktop-beta and continue:

$ curl -sLO
$ sha256sum signal-desktop-beta_1.1.0-beta.6_amd64.deb 
a38eb35001618019affba7df4e54ccbb36581d232876e0f1af9622970b38aa12  signal-desktop-beta_1.1.0-beta.6_amd64.deb
To extract the package, we'll need the dpkg package:

$ sudo dnf install dpkg
$ dpkg -x signal-desktop-beta_1.1.0-beta.6_amd64.deb deb
Check if all libraries are installed:

$ ldd deb/opt/Signal\ Beta/signal-desktop-beta | grep not
Looks good - let's "install" the package in /opt now:
sudo mv deb/opt/Signal\ Beta /opt/
sudo chown -R root:root /opt/Signal\ Beta/
sudo ln -s /opt/Signal\ Beta/signal-desktop-beta /usr/local/bin/signal-desktop-beta
Create desktop shortcut and icons:

mv deb/usr/share/applications/signal-desktop-beta.desktop ~/.local/share/applications/signal-desktop-beta.desktop
rsync -av deb/usr/share/icons/hicolor/ ~/.local/share/icons/hicolor/
The .desktop file should contain something like this:

$ cat  ~/.local/share/applications/signal-desktop-beta.desktop
[Desktop Entry]
Name=Signal Desktop Beta
Comment=Private messaging from your desktop
Exec="/opt/Signal Beta/signal-desktop-beta" %U
With all that in place, Signal Desktop Beta should be ready to go. Don't forget to migrate the data from the old installation!

Build from source

Building from source may need a ton of dependencies, so it may or may not be desirable to install all that on a desktop system. The short version of the install routine would be:

git clone Signal-Desktop-git
cd Signal-Desktop-git

yarn config set cache-folder /usr/local/src/tmp/yarn/
npm config set cache /usr/local/src/tmp/npm/
TMPDIR=/usr/local/src/tmp/ npm install
So far, so good, but then there's some grunt breakage:

$ node_modules/grunt-cli/bin/grunt 
Loading "sass.js" tasks...ERROR
>> Error: ENOENT: no such file or directory, scandir '../node_modules/node-sass/vendor'
Loading "sass.js" tasks...ERROR
>> Error: ENOENT: no such file or directory, scandir '../node_modules/node-sass/vendor'
Warning: Task "sass" not found. Use --force to continue.

Aborted due to warnings.
...TBD :-\

Compression benchmarks 2017

As I had to send a disk based backup to another machine on a local network, I wanted to compress the backup data before sending it over the wire, of course. And as the last benchmark has been done one year ago, it was time for another one anyway :-)

$ ls -hgo disk.img
 -rw------- 1 861M Oct 25 23:02 disk.img

$ ./ -n 3 -f disk.img | tee foo.out

$ ./ -r foo.out
### Fastest compressor:
### pzstd/1c:      .75 seconds / 61.900% smaller 
### pigz/1c:      3.25 seconds / 60.100% smaller 
### zstd/1c:      3.25 seconds / 62.000% smaller 
### bro/1c:       3.50 seconds / 59.500% smaller 
### pzstd/9c:     6.00 seconds / 67.700% smaller 
### pigz/9c:     11.00 seconds / 63.800% smaller 
### gzip/1c:     12.00 seconds / 59.900% smaller 
### zstd/9c:     17.50 seconds / 68.000% smaller 
### pbzip2/9c:   18.00 seconds / 67.400% smaller 
### pbzip2/1c:   27.50 seconds / 64.900% smaller 
### lzma/1c:     53.50 seconds / 68.700% smaller 
### xz/1c:       54.75 seconds / 68.700% smaller 
### gzip/9c:     65.00 seconds / 63.700% smaller 
### bzip2/1c:    66.00 seconds / 64.900% smaller 
### bzip2/9c:    66.00 seconds / 67.500% smaller 
### bro/9c:      83.25 seconds / 70.500% smaller 
### lzma/9c:    240.50 seconds / 76.700% smaller 
### xz/9c:      243.75 seconds / 76.700% smaller 

### Smallest size:
### xz/9c:      243.75 seconds / 76.700% smaller 
### lzma/9c:    240.50 seconds / 76.700% smaller 
### bro/9c:      83.25 seconds / 70.500% smaller 
### xz/1c:       54.75 seconds / 68.700% smaller 
### lzma/1c:     53.50 seconds / 68.700% smaller 
### zstd/9c:     17.50 seconds / 68.000% smaller 
### pzstd/9c:     6.00 seconds / 67.700% smaller 
### bzip2/9c:    66.00 seconds / 67.500% smaller 
### pbzip2/9c:   18.00 seconds / 67.400% smaller 
### pbzip2/1c:   27.50 seconds / 64.900% smaller 
### bzip2/1c:    66.00 seconds / 64.900% smaller 
### pigz/9c:     11.00 seconds / 63.800% smaller 
### gzip/9c:     65.00 seconds / 63.700% smaller 
### zstd/1c:      3.25 seconds / 62.000% smaller 
### pzstd/1c:      .75 seconds / 61.900% smaller 
### pigz/1c:      3.25 seconds / 60.100% smaller 
### gzip/1c:     12.00 seconds / 59.900% smaller 
### bro/1c:       3.50 seconds / 59.500% smaller 

### Fastest decompressor:
### pzstd/dc:      .25 seconds
### zstd/dc:      1.00 seconds
### bro/dc:       2.25 seconds
### pigz/dc:      2.75 seconds
### gzip/dc:      4.25 seconds
### pbzip2/dc:    5.00 seconds
### lzma/dc:     14.25 seconds
### xz/dc:       15.25 seconds
### bzip2/dc:    20.75 seconds
Now the only thing left is to extend our little benchmark scripts to actually compare these to last year's results...

So, while this site cannot be equipped with any kind of TLS certificates (don't ask), I'm using Let's Encrypt certificates for some other web sites. But as much as I like everything the EFF does, I despise their official LE client, for apparent reasons:

$ sudo apt-get install certbot
The following NEW packages will be installed:
  certbot python-acme python-certbot python-cffi-backend python-configargparse python-configobj python-cryptography python-enum34 python-funcsigs python-idna python-ipaddress
  python-mock python-openssl python-parsedatetime python-pbr python-pyasn1 python-requests python-rfc3339 python-six python-tz python-urllib3 python-zope.component
  python-zope.event python-zope.hookable python-zope.interface
0 upgraded, 25 newly installed, 0 to remove and 3 not upgraded.
No, thank you :-\ Luckily, their ACME protocol allows for many more client options to choose from. After some experiments, I almost settled for, but ran into unfixed bugs and ended up with a fork of the same. With that, I wanted to cover two use cases:

Local server

In this scenario, the client is requesting (and validating) certificates for the same machine it's running on. This is also the machine where our account key resides. The work flow is basically:
## Needs to be done only once:
$ register -a letsencrypt-account-key.pem \

$ umask 0022
$ sign -a letsencrypt-account-key.pem \
      -k letsencrypt-example-key.pem \
      -w /var/www/.well-known/acme-challenge/ \
      -c letsencrypt-$(date -I)-example-cert.pem
The well-known path should be writeable by the user executing the script and readable by the webserver. That way, we don't have to play funky games with our webserver configuration, trying to generate the responses dynamically but instead we (temporarily) create actual files in that directory to be validated in the process. This may not work when renewing certificates for different domains, though.

We may need the full certificate chain (and some DH parameters too), so let's concatenate them altogether:
$ cat letsencrypt-$(date -I)-example-cert.pem \
      letsencrypt-$(date -I)-example-cert.pem_chain \
      dhparams-2048.pem \
      > letsencrypt-$(date -I)-example-cert-combined.pem
The resulting file can then be installed as SSLCertificateFile or ssl_certificate or ssl_cert or whatever service is in use here.

Remote server

While the client seems small enough, we still don't want to install it on every server that needs a certificate. Instead, we'll use to issue certificates for a remote machine. However, as the certificates are domain-validated, we need a way to transfer the validation token to the remote server. Luckily, this version of is able to do just that:
$ sign -a letsencrypt-account-key.pem \
      -k letsencrypt-foobar-key.pem \
      -P /usr/local/bin/push-response-ssh \
      -c letsencrypt-$(date -I)-foobar-cert.pem
Here, a hook script is transferring the token to the remote server (configured in the same script). On the remote side, another hook will read the validation token from stdin and install it in its own well-known location (TOKEN_DIR). This can all be configured with SSH key authentication:
foobar$ cat ~www-data/.ssh/authorized_keys 
command="/usr/local/sbin/push-response-ssh-remote" ssh-ed25519 AAAAC3[...] admin@local

foobar$ grep ^TOKEN_DIR /usr/local/sbin/push-response-ssh-remote 
The resulting certificate is still installed locally and needs to be transferred to the remote side. Since we configured the remote www-data account to only allow the hook script to execute, we have adjusted the same somewhat to allow the certificate to be installed by the same user. Since we're now abusing the original hook script (and multiple command directives for a single key are not supported), our deployment command looks somewhat convoluted:
$ cat letsencrypt-foobar-key.pem \
      letsencrypt-$(date -I)-foobar-cert.pem{,_chain} | \
      ssh -i ~/.ssh/letsencrypt-key \
      installkey \ \
      $(openssl rand -hex 32 | cut -c-43) \
      $( thumbprint -a letsencrypt-account-key.pem | awk '{print $NF}')
So, the new installkey parameter tells the remote hook script what to do. The and the random value are just place holders for a valid domain name resp. something that looks like a validation token. This is all because push-response-ssh-remote expects all these things. The deployment would be much easier if we 1) used a different user or key or 2) re-write the remote hook to allow for a simpler deployment :-)

With that in place, the certificate for the remote side has been saved to whatever is configured in push-response-ssh-remote and can now be used in the respective services. Yay! \o/

Of character and block devices

While playing around with an OpenBSD system, I came across the different represenation of disk devices in BSD systems again:

$ ls -l /dev/{r,}wd0c
crw-r-----  1 root  operator   11,   2 Jun 28 02:22 /dev/rwd0c
brw-r-----  1 root  operator    0,   2 Jun 28 02:22 /dev/wd0c

$ pv -Ss 200m < /dev/wd0c > /dev/null  
 200MiB 0:00:11 [17.5MiB/s] [==================>] 100%

$ pv -Ss 200m < /dev/rwd0c > /dev/null 
 200MiB 0:00:03 [56.4MiB/s] [==================>] 100%
The FreeBSD Architecture Handbook documents this quite nicely:

  > Block devices are disk devices for which the kernel provides
  > caching. This caching makes block-devices almost unusable,
  > or at least dangerously unreliable. The caching will reorder
  > the sequence of write operations, depriving the application of
  > the ability to know the exact disk contents at any one instant
  > in time.
In short: don't use block devices on BSD systems but use their raw (character) devices instead, at least when accessing them directly.

Ext4 on MacOS X

With the new Raspberry Pi 3 Model B at hand and Raspbian already running, I wanted to see if the AArch64 port of Arch Linux would run as well. As I didn't have a real computer available at that time, I tried to get the image on the microSD card on MacOS .

First, let's unmount (but not eject) the microSD card:
$ diskutil umountDisk disk2
Unmount of all volumes on disk2 was successful
Create two partitions on the device:
$ sudo fdisk -e /dev/rdisk2
fdisk: 1> erase
fdisk:*1> edit 1
Partition id ('0' to disable)  [0 - FF]: [0] (? for help) 0B
Do you wish to edit in CHS mode? [n] 
Partition offset [0 - 31116288]: [63] 
Partition size [1 - 31116225]: [31116225] 204800

fdisk:*1> edit 2
Partition id ('0' to disable)  [0 - FF]: [0] (? for help) 83
Do you wish to edit in CHS mode? [n] 
Partition offset [0 - 31116288]: [204863] 
Partition size [1 - 30911425]: [30911425] 

fdisk:*1> p
Disk: /dev/rdisk2       geometry: 1936/255/63 [31116288 sectors]
Offset: 0       Signature: 0xAA55
         Starting       Ending
 #: id  cyl  hd sec -  cyl  hd sec [     start -       size]
 1: 0B    0   1   1 - 1023 254  63 [        63 -     204800] Win95 FAT-32
 2: 83 1023 254  63 - 1023 254  63 [    204863 -   30911425] Linux files*
 3: 00    0   0   0 -    0   0   0 [         0 -          0] unused      
 4: 00    0   0   0 -    0   0   0 [         0 -          0] unused      
fdisk:*1> write
Writing MBR at offset 0.
fdisk: 1> quit
Create a file system on each partition (we'll need e2fsprogs to create an ext4 file system):
$ sudo newfs_msdos -v boot /dev/rdisk2s1
$ sudo /opt/local/sbin/mkfs.ext4 /dev/rdisk2s2 
As MacOS is able to read FAT-32, we should be able to mount it right away:
$ diskutil mount disk2s1
Volume BOOT on disk2s1 mounted

$ df -h /Volumes/BOOT
Filesystem     Size   Used  Avail Capacity  Mounted on
/dev/disk2s1  100Mi  762Ki   99Mi     1%    /Volumes/BOOT
Mounting a ext4 file systems turned out to be more difficult and there are several solutions available.


ext2fuse is said to provide ext2/ext3 support via FUSE, but it segfaults on our newly created ext4 file system:
$ sudo /opt/local/bin/ext2fuse /dev/disk2s2 /mnt/disk
/dev/disk2s2 is to be mounted at /mnt/disk
fuse-ext2fs: Filesystem has unsupported feature(s) while trying to open /dev/disk2s2
Segmentation fault: 11

$ mount | tail -1
/dev/disk2s2 on /mnt/disk (osxfuse, synchronous)

$ df -h /mnt/disk
Filesystem     Size   Used  Avail Capacity  Mounted on
/dev/disk2s2    0Bi    0Bi    0Bi   100%    /mnt/disk

$ touch /mnt/disk/foo
touch: /mnt/disk/foo: Device not configured
Maybe ext4 is just too new for ext2fuse, let's try with ext2 instead:
$ sudo /opt/local/sbin/mkfs.ext2 /dev/rdisk2s2
$ sudo /opt/local/bin/ext2fuse /dev/disk2s2 /mnt/disk
/dev/disk2s2 is to be mounted at /mnt/disk
fuse-ext2 initialized for device: /dev/disk2s2
block size is 4096
ext2fuse_dbg_msg: File not found by ext2_lookup while looking up "DCIM"
ext2fuse_dbg_msg: File not found by ext2_lookup while looking up "VSCAN"
ext2fuse_dbg_msg: File not found by ext2_lookup while looking up "DCIM"
ext2fuse_dbg_msg: File not found by ext2_lookup while looking up ".Spotlight-V100"
ext2fuse_dbg_msg: File not found by ext2_lookup while looking up ".metadata_never_index"
This command never completes but could be terminated with ^C. The same happens with an ext3 file system.


ext4fuse aims for ext4 support via FUSE, let see how that goes:
$ sudo /opt/local/sbin/mkfs.ext4 /dev/rdisk2s2
$ sudo /opt/local/bin/ext4fuse /dev/disk2s2 /mnt/disk 
$ mount | tail -1
ext4fuse@osxfuse0 on /mnt/disk (osxfuse, synchronous)

$ df -h /mnt/disk
Filesystem          Size   Used  Avail Capacity  Mounted on
ext4fuse@osxfuse0    0Bi    0Bi    0Bi   100%    /mnt/disk

$ sudo touch /mnt/disk/foo
touch: /mnt/disk/foo: Function not implemented
So close! :-) But there's no write support for ext4fuse yet.


There's another option, called fuse-ext2 which appears to feature (experimental) write support. We'll need FUSE for macOS again and then build fuse-ext2 from scratch:
$ sudo port install e2fsprogs
$ git clone fuse-ext2-git
$ cd $_
$ ./ && LDFLAGS="-L/opt/local/lib" CFLAGS="-I/opt/local/include" \
    ./configure --prefix=/opt/fuse-ext2
$ make && sudo make install
So, let's try:
$ sudo /opt/fuse-ext2/bin/fuse-ext2 /dev/rdisk2s2 /mnt/disk -o rw+
Rats - a window pops up with:
FUSE-EXT2 could not mount /dev/disk2s2
at /mnt/disk/ because the following problem occurred:
But the error description is empty, and there's nothing in the syslog too. After some digging I decided to reboot and this time it worked:
$ sudo /opt/fuse-ext2/bin/fuse-ext2 /dev/rdisk2s2 /mnt/disk -o rw+
$ mount | tail -1
/dev/rdisk2s2 on /mnt/disk (osxfuse_ext2, local, synchronous)

$ df -h /mnt/disk/
Filesystem      Size   Used  Avail Capacity  Mounted on
/dev/rdisk2s2   15Gi  104Mi   14Gi     1%    /mnt/disk

$ sudo touch /mnt/disk/foo
$ ls -l /mnt/disk/foo
-rw-r--r--  1 root  wheel  0 Mar  5 14:29 /mnt/disk/foo
That should be enough for us to finally install the ArchLinux image on that microSD card:
$ tar -C /Volumes/BOOT/ -xzf ArchLinuxARM-rpi-3-latest.tar.gz boot
$ mv /Volumes/BOOT/{boot/*,} && rmdir /Volumes/BOOT/boot
And for the root file system:
$ sudo tar --exclude="./boot" -C /mnt/disk/ -xvzf ArchLinuxARM-rpi-3-latest.tar.gz 
x ./bin
x ./dev/: Line too long
tar: Error exit delayed from previous errors.
Apparently bsdtar has trouble when the --exclude switch is used, so let's try without and remove the superfluous /boot contents later:
$ sudo tar -C /mnt/disk/ -xzf ArchLinuxARM-rpi-3-latest.tar.gz
$ sudo rm -r /mnt/disk/boot/*
This takes quite a long while to complete, but completed eventually. Of course, all this could be avoided if would have used another operating system in the first place :-)

tr: Bad String

Trying to mangle some characters resulted in a weird error message:
$ echo hello | tr [:lower:] [:upper:]
Bad string
Huh? Before debugging any further, searching the interwebs returns quite a few results, of course, so let's look at our options then:

$ type tr
tr is /usr/bin/tr

$ find /usr -type f -perm -0500 -name tr -ls 2>/dev/null
32054   11 -rwxr-xr-x   1 root bin  9916 Jan 23  2005 /usr/ucb/tr
16674   19 -r-xr-xr-x   1 root bin 18540 Jan 23  2005 /usr/xpg6/bin/tr
  410   20 -r-xr-xr-x   1 root bin 19400 Jan 23  2005 /usr/bin/tr
75251   19 -r-xr-xr-x   1 root bin 18520 Jan 23  2005 /usr/xpg4/bin/tr
Besides our default from SUNWcsu, we have three other versions of tr(1) available. The UCB version tries do do...something:

$ echo hello | /usr/ucb/tr [:lower:] [:upper:]
Apparently it replaces each character (position) literally, but fails to recognize the bracket expressions. Since the UCB tools were removed in later versions anyway, let's skip that for now. The two X/Open versions seem to manage:

$ echo hello | /usr/xpg6/bin/tr [:lower:] [:upper:]

$ echo hello | /usr/xpg4/bin/tr [:lower:] [:upper:]
But why wouldn't it work with the SUNWcsu version? truss(1) reports a missing file, but this turns out to be a red herring:

$ echo hello | truss -elfda tr [[:lower:]] [[:upper:]]
Base time stamp:  1481011767.7308  [ Tue Dec  6 09:09:27 MET 2016 ]
26125/1:         0.0000 execve("/usr/bin/tr", 0xFFBFFC9C, 0xFFBFFCAC)  argc = 3
26125/1:         argv: tr [[:lower:]] [[:upper:]]
26125/1:         envp: LC_MONETARY=en_GB.ISO8859-15 TERM=xterm SHELL=/bin/bash
26125/1:          LC_NUMERIC=en_GB.ISO8859-15 LC_ALL=en_US.UTF-8
26125/1:          LC_MESSAGES=C LC_COLLATE=en_GB.ISO8859-15 LANG=en_US.UTF-8
26125/1:          LC_CTYPE=en_GB.ISO8859-1 LC_TIME=en_GB.ISO8859-15
26125/1:         0.0061 stat64("/usr/lib/locale/en_US.UTF-8/", 0xFFBFE8D0) Err#2 ENOENT
26125/1:         0.0063 open("/usr/lib/locale/en_US.UTF-8/LC_MESSAGES/", O_RDONLY) Err#2 ENOENT
26125/1:         0.0064 fstat64(2, 0xFFBFEA38)                          = 0
Bad string
26125/1:         0.0064 write(2, " B a d   s t r i n g\n", 11)          = 11
26125/1:         0.0065 _exit(1)
(Un)fortunately I had my share of weird experiences with character encodings and the like. And indeed, if we use a single-byte locale, /usr/bin/tr works just fine:

$ echo $LC_ALL

$ echo hello | LC_ALL=en_US tr [[:lower:]] [[:upper:]]
Another workaround would be to use another expression, if possible:

$ echo hello | tr [a-z] [A-Z]
In newer SunOS versions, /usr/bin/tr has been fixed and works as expected.

Encrypted network block device

While backing up with Crashplan works fine most of the time (and one trusts their zero-knowledge promise), sometimes new software updates, power outages or other unplanned interruptions cause Crashplan to fail and either stop backing up or discard the whole archive and start to backup from scratch, uploading the whole disk again :-\

So yeah, it mostly works but somehow I'd like to be a bit more in control of things. The easiest thing would be to order some disk space in the cloud and rsync all data off to a remote location - but of we need to encrypt it first. But how? There are a few solutions I've came across so far, I'm sure there are others, but let's look at them real short:

  • duplicity uses librsync to upload GnuPG encrypted parts to the remote destination. I've heard good (and bad) things about it, but the tought of splitting up data into small chunks and encrypting it, uploading thousands of small bits of random-looking data sounds cool and a bit frightening at the same time. Especially the restore scenario boggles my mind. I don't want to dismiss this entirely (and may even come back to it later on), but let's look for something saner for now.

  • Attic is a deduplicating backup program written in Python. I've haven't actually tried this one either, although it seems to support encryption and remote backup destinations, although the mentioning of FUSE mounts make me a bit uneasy.

  • Obnam supports encrypted remote backups, again via GnuPG. I gotta check this out if this really works as advertised.

  • Burp uses librsync and supports something called "client side file encryption" - but that turns off "delta differencing", which sounds like the whole purpose of using librsync in the first place is then gone.

  • Rclone supports encrypted backups, but only to some pre-defined storage providers and not to arbitrary SSH-accessible locations.

  • BorgBackup has the coolest name (after Obnam :-)) and supports deduplication, compression and authenticated encryption - almost too good to be true. This should really be my go-to-solution for my usecase and if my hand-stitched version isn't working out, I'll come back to this for sure.

With that, let's see if we can employ a Network Block Device to serve our needs.
As an example, let's install nbd-server on the remote location and set up a disk that we want to serve to our backup client later on:
$ sudo apt-get install nbd-server

$ cd /etc/nbd-server/
$ grep -rv ^\# .
./config:       user = nbd
./config:       group = nbd
./config:       listenaddr = localhost
./config:       allowlist = true
./config:       includedir = /etc/nbd-server/conf.d
./conf.d/local.conf:    exportname = /dev/loop1
./conf.d/local.conf:    flush = true
./conf.d/local.conf:    readonly = false
./conf.d/local.conf:    authfile = /etc/nbd-server/allow
We will of course serve a real disk later on, but for now a loop device will do:
$ dd if=/dev/zero bs=1M count=10240 | pv | sudo dd of=/var/tmp/test.img
$ sudo losetup -f /var/tmp/test.img
With that, our nbd-server can be started and should listen on localhost only - we'll use SSH port-forwarding later on to connect back to this machine:
$ ss -4lnp | grep nbd
tcp LISTEN  0 10 *:* users:(("nbd-server",pid=9249,fd=3))
The client side needs a bit more work. An SSH tunnel of course, but also the nbd kernel module and the nbd-client program. However, I noticed that the nbd-client version that comes with Debian/8.0 contained an undocumented bug that made it impossible to gain write access to the export block device. And we do really want write access :-) Off to the source, then:
$ sudo apt-get install libglib2.0-dev
$ git clone nbd-git && cd nbd-git
While the repository appears to be maintained, the build system looks kinda archaic. And we don't want to install almost 200 MB in dependencies for the docbook-utils packages to provide /usr/bin/docbook2man to build man pages. So let's skip all that and build only the actual programs:
$ sed -r '/^make -C (man|systemd)/d' -i
$ sed    '/man\/nbd/d;/systemd\//d'  -i

$ ./
$ ./configure --prefix=/opt/nbd --enable-syslog
$ make && sudo make install
The configuration file format changed (again) or be passed on the command line:
$ sudo modprobe nbd
$ sudo /opt/nbd/sbin/nbd-client -name testdisk localhost 10809 /dev/nbd0 -timeout 30 -persist
On the server side, this is noticed too:
nbd_server[9249]: Spawned a child process
nbd_server[9931]: virtstyle ipliteral
nbd_server[9931]: connect from, assigned file is /dev/loop1
nbd_server[9931]: Starting to serve
nbd_server[9931]: Size of exported file/device is 10737418240
We can now use /dev/nbd0 as if it were a local disk. We'll create a key, initialize dm-crypt and create a file system:
$ openssl rand 4096 | gpg --armor --symmetric --cipher-algo aes256 --digest-algo sha512 > testdisk-key.asc
$ gpg -d testdisk-key.asc | sudo cryptsetup luksFormat --cipher twofish-cbc-essiv:sha256 \
                  --hash sha256 --key-size 256 --iter-time=5000 /dev/nbd0
gpg: AES256 encrypted data
Enter passphrase: XXXXXXX
gpg: encrypted with 1 passphrase

$ gpg -d testdisk-key.asc | sudo cryptsetup open --type luks /dev/nbd0 testdisk
$ sudo file -Ls /dev/nbd0 /dev/mapper/testdisk
/dev/nbd0:            LUKS encrypted file, ver 1 [twofish, cbc-essiv:sha256, sha256] UUID: 30f41e4...]
/dev/mapper/testdisk: data

$ sudo cryptsetup status testdisk
/dev/mapper/testdisk is active.
  type:    LUKS1
  cipher:  twofish-cbc-essiv:sha256
  keysize: 256 bits
  device:  /dev/nbd0
  offset:  4096 sectors
  size:    20967424 sectors
  mode:    read/write

$ sudo mkfs.xfs -m crc=1,finobt=1 /dev/mapper/testdisk
$ sudo mount -t xfs /dev/mapper/testdisk /mnt/disk/
$ df -h /mnt/disk
Filesystem            Size  Used Avail Use% Mounted on
/dev/mapper/testdisk   10G   33M   10G   1% /mnt/disk
Deactivate with:
$ sudo umount /mnt/disk 
$ sudo cryptsetup close testdisk
$ sudo pkill -f /opt/nbd/sbin/nbd-client
When mounted, the disk speed is limited of course by the client's upload speed and the CPU speed too (for SSH and dm-crypt). Let's play with this for a while and see how this works out with rsync workloads. Maybe I'll come back for BorgBackup after all :-)

Weird CDROM formats

So, I came across these files:
$ ls -goh
-rw-r--r-- 1 526M Sep 29 12:58 file.bin
-rw-r--r-- 1  478 Sep 29 12:50 file.cue
Does anyone remember cue sheets? Luckily, even today there are tools out there to make sense of these and convert them into something usable:
$ bchunk -v file.bin file.cue file.iso
Reading the CUE file:

Track  1: MODE1/2352    01 00:00:00 (startsect 0 ofs 0)
Track  2: AUDIO     01 22:46:13 (startsect 102463 ofs 240992976)
Track  3: AUDIO     01 25:25:74 (startsect 114449 ofs 269184048)
Track  4: AUDIO     01 28:01:35 (startsect 126110 ofs 296610720)
Track  5: AUDIO     01 31:14:31 (startsect 140581 ofs 330646512)
Track  6: AUDIO     01 34:51:35 (startsect 156860 ofs 368934720)
Track  7: AUDIO     01 37:51:22 (startsect 170347 ofs 400656144)
Track  8: AUDIO     01 41:22:03 (startsect 186153 ofs 437831856)
Track  9: AUDIO     01 44:18:34 (startsect 199384 ofs 468951168)
Track 10: AUDIO     01 46:38:03 (startsect 209853 ofs 493574256)
Track 11: AUDIO     01 49:12:05 (startsect 221405 ofs 520744560)

Writing tracks:

 1: file.iso01.iso
 mmc sectors 0->102462 (102463)
 mmc bytes 0->240992975 (240992976)
 sector data at 16, 2048 bytes per sector
 real data 209844224 bytes
 200/200  MB  [********************] 100 %

 2: file.iso02.cdr
 mmc sectors 102463->114448 (11986)
 mmc bytes 240992976->269184047 (28191072)
 sector data at 0, 2352 bytes per sector
 real data 28191072 bytes
  26/26   MB  [********************] 100 %
 3: file.iso03.cdr
In this case, we don't care for the audio part of the image, so we could discard all the .cdr files later on and just use the ISO image:
$ ls -goh file.*
-rw-r--r-- 1 526M Sep 29 12:58 file.bin
-rw-r--r-- 1  478 Sep 29 12:50 file.cue
-rw-r--r-- 1 201M Oct 31 16:01 file.iso01.iso

$ sudo mount -t iso9660 -o loop,ro file.iso01.iso /mnt/cdrom
$ ls /mnt/cdrom
AUTORUN.INF  Data  Install  readme.txt  Setup.exe  Splash
Oh, yeah :-)

Compression benchmarks 2016

Some time has passed since the last compression benchmarks and new contenders entered the race, so let's do another round of benchmarks, shall we?

MacBook Pro 2009

This laptop ships with an Intel Core2 Duo P8700 processor, so these tests may take a while:
$ tar -cf test.tar /usr/share/ 
$ ls -goh test.tar
-rw-r--r--  1    384M Oct  6 08:00 test.tar

$ time for i in {1..10}; do ~/bin/ test.tar | tee results_${i}.out; done
real    2046m5.142s
user    222m1.302s
sys     3m30.933s
So, 10 rounds of compressing and decompressing this tarball took 34 hours to complete. The results break down to:
$ for o in 9c 1c dc; do
   for p in gzip pigz bzip2 pbzip2 xz lzma zstd pzstd brotli; do
      awk "/"$p"\/"$o"/ {sum+=\$3} END {print \"$p/$o\t\", sum/10}" results_*.out
   done | sort -nk2; echo
pzstd/9c         19.7
zstd/9c          53.4
brotli/9c       234.5
pigz/9c         746.4
pbzip2/9c       764.6
gzip/9c         775.2
lzma/9c        1180.2
bzip2/9c       1563.9
xz/9c          3825

pzstd/1c          2.4
brotli/1c         4.7
zstd/1c           6.1
pigz/1c           6.2
gzip/1c          10.4
pbzip2/1c       752
xz/1c           778.7
lzma/1c         779.5
bzip2/1c       1532.3

pzstd/dc          0.8
zstd/dc           1.8
gzip/dc           2.4
pigz/dc           2.4
brotli/dc         2.9
pbzip2/dc         9.1
lzma/dc          10.2
xz/dc            10.8
bzip2/dc        748

Thinkpad E431

This machine comes with an i7-3632QM CPU and our test tarball is somewhat bigger:
$ tar -cf test.tar /usr/share/locale/ /usr/share/games/quake3/
$ ls -goh test.tar
-rw------- 1 978M Oct  8 22:38 test.tar

$ time for i in {1..10}; do ~/bin/ test.tar | tee results_${i}.out; done
real	420m39.764s
user	529m13.192s
sys	3m46.148s
After 7 hours, the results are in:
$ for o in 9c 1c dc; do
    for p in gzip pigz bzip2 pbzip2 xz lzma zstd pzstd brotli; do
       awk "/"$p"\/"$o"/ {sum+=\$3} END {print \"$p/$o\t\", sum/10}" results_*.out
    done | sort -nk2; echo
pzstd/9c	 17.4
pigz/9c	         17.5
pbzip2/9c	 31.5
zstd/9c    	 70.4
gzip/9c    	 84.4
bzip2/9c	145.3
brotli/9c	260
xz/9c	        612.4
lzma/9c	        622.4

pzstd/1c 	  3.3
pigz/1c	          7.2
brotli/1c	  8
zstd/1c	         10.2
pbzip2/1c	 26
gzip/1c	         27.8
bzip2/1c	141.6
lzma/1c	        181.5
xz/1c	        185.2

pzstd/dc	  0.6
zstd/dc	          2.1
brotli/dc	  4.8
pigz/dc	          5
gzip/dc	          8
pbzip2/dc	  8.8
xz/dc	         36.5
lzma/dc	         40.2
bzip2/dc	 53.3

PowerBook G4

This (older) machine is still running 24/7, so let's see which compressor we should use in the future:
$ tar -cf test.tar /usr/share/doc/gcc-4.9-base/ /usr/share/perl5
$ ls -goh test.tar
-rw-r--r-- 1 41M Oct 15 02:53 test.tar

$ PROGRAMS="gzip bzip2 xz lzma brotli zstd" \
  ~/bin/ -n 10 -f test.tar | tee ~/r.log
$ ~/bin/ -r ~/r.log
### Fastest compressor:
### zstd/1c:      1.90 seconds / 63.300% smaller 
### brotli/1c:    2.20 seconds / 57.900% smaller 
### gzip/1c:      4.80 seconds / 58.800% smaller 
### zstd/9c:     11.30 seconds / 66.000% smaller 
### gzip/9c:     19.00 seconds / 62.500% smaller 
### bzip2/1c:    36.90 seconds / 63.800% smaller 
### lzma/1c:     37.80 seconds / 65.700% smaller 
### xz/1c:       40.20 seconds / 66.000% smaller 
### brotli/9c:   60.50 seconds / 66.800% smaller 
### bzip2/9c:    63.00 seconds / 66.000% smaller 
### xz/9c:      111.90 seconds / 68.000% smaller 
### lzma/9c:    115.90 seconds / 67.700% smaller 

### Smallest size:
### zstd/9c:     11.30 seconds / 66.000% smaller 
### zstd/1c:      1.90 seconds / 63.300% smaller 
### xz/9c:      111.90 seconds / 68.000% smaller 
### xz/1c:       40.20 seconds / 66.000% smaller 
### lzma/9c:    115.90 seconds / 67.700% smaller 
### lzma/1c:     37.80 seconds / 65.700% smaller 
### gzip/9c:     19.00 seconds / 62.500% smaller 
### gzip/1c:      4.80 seconds / 58.800% smaller 
### bzip2/9c:    63.00 seconds / 66.000% smaller 
### bzip2/1c:    36.90 seconds / 63.800% smaller 
### brotli/9c:   60.50 seconds / 66.800% smaller 
### brotli/1c:    2.20 seconds / 57.900% smaller 

### Fastest decompressor:
### zstd/dc:       .80 seconds
### brotli/dc:    1.20 seconds
### gzip/dc:      1.20 seconds
### xz/dc:        1.70 seconds
### lzma/dc:      3.20 seconds
### bzip2/dc:     7.20 seconds

Building NRPE for OpenWRT

In the last article we restored nrpe from backups to a running OpenWRT installation. After another power outage we have to do this again, but let's actually build nrpe this time and only restore its configuration from the backup.

The build process will happen in a VM running Debian/jessie(amd64), so missing utilities or header files will have to be installed via apt-get:
sudo apt-get install autoconf binutils build-essential docbook gawk gettext git libncurses5-dev libssl-dev libz-dev ncurses-term openssl sharutils subversion unzip
We'll check out the source and switch to the v15.05.1 branch, because we'll need to build for the release that's currently running on the router. Since OpenWrt switched to musl last year, we cannot build trunk as the running Chaos Calmer is still linked against uClibc.
git clone openwrt-git
cd $_
git checkout -b local v15.05.1
Note: the branch does no longer exist!

Fetch an appropriate .config (again, we cannot use trunk just yet) and enter the configuration menu:
wget -O .config
make defconfig
make menuconfig
Here, we'll select our target profile and disable the SDK:
  • Target Profile => NETGEAR WNDR3700/WNDR3800/WNDRMAC
  • [_] Build the OpenWrt SDK (disabled)
Let's also disable all modular packages from the build and run the prerequisite check to verfiy that the configuration is still valid:
sed 's/=m$/=n/' -i.bak .config
make prereq
With that, we're ready to build and install the toolchain:
script -c "time make -j4 V=s tools/install && date && time make -j4 V=s toolchain/install" ~/build.log 
This will need some time (and diskspace) to complete. Once completed (check the build.log!), we can finally build our packages:
wget -O ~/
(cd /tmp && unzip ~/ && (cd /tmp/openwrt-master/ && tar -cf - package) | tar -xvf -
make oldconfig
script -c "time make -j4 V=s package/nrpe/compile" -a ~/build.log
script -c "time make -j4 V=s package/monitoring-plugins/compile" -a ~/build.log
Note: this will build all dependencies as well:
$ grep -h DEP package/network/utils/{monitoring-plugins,nrpe}/Makefile 
  DEPENDS:=+libopenssl +libpthread
  DEPENDS:=+libopenssl +libwrap
When everything is built correctly, we should have two package files:
$ ls -hgotr bin/ar71xx/packages/base/
total 1.1M
-rw-r--r-- 1  35K Oct  2 13:10 libgcc_5.3.0-1_ar71xx.ipk
-rw-r--r-- 1 268K Oct  2 13:10 libc_1.1.15-1_ar71xx.ipk
-rw-r--r-- 1  857 Oct  2 13:10 libpthread_1.1.15-1_ar71xx.ipk
-rw-r--r-- 1  36K Oct  2 13:11 zlib_1.2.8-1_ar71xx.ipk
-rw-r--r-- 1 741K Oct  2 13:16 libopenssl_1.0.2j-1_ar71xx.ipk
-rw-r--r-- 1  24K Oct  2 13:17 nrpe_3.0.1-1_ar71xx.ipk
-rw-r--r-- 1 768K Oct  2 13:32 monitoring-plugins_2.2-1_ar71xx.ipk

$ file build_dir/target-mips*/*/src/nrpe
build_dir/target-mips_34kc_uClibc- ELF 32-bit MSB executable, MIPS, MIPS32 rel2 version 1, dynamically linked, interpreter /lib/, not stripped
The installation should automatically install any dependencies, if needed:
router$ opkg install ./*.ipk
Installing monitoring-plugins (2.1.2-1) to root...
Installing nrpe (3.0.1-1) to root...

router$ /etc/init.d/nrpe enable
router$ /etc/init.d/nrpe start

router$ netstat -lnp | grep 5666
tcp 0 0* LISTEN 6771/nrpe
This was the easy part. The difficult part will be to get both packages upstream :-)