ygoe's questions

I'm not sure I completely understood the whole relationships between ifupdown, systemd-networkd and netplan. I think netplan transforms its YAML configuration into a more verbose systemd-network configuration that I could also maintain myself. Does this have anything to do with the classic ifupdown way and /etc/network/interfaces? I don't know how the tools behind the old solution are called, I just know that /etc/network/interfaces was the place to set things up. Some magic tools would read that file and do something.

So now I face the situation that Ubuntu 20.04 comes with netplan but that doesn't support additional IPv6 addresses with preferred_lft=0, a feature I need today. So I cannot use netplan for that. systemd-network doesn't seem to allow multiple matching config files for one interface, so I think I must not use netplan at all.

Now the question is: where should I go to? Can I keep systemd-network and maintain that config file fully myself? Or do I have to (or should I, and why) go all the way back to /etc/network/interfaces and ifupdown?

There are a number of tutorials and answers available that explain the way back to ifupdown, not mentioning systemd-network at all. So I don't know whether that would be a viable option, maybe a more future-proof one (ifupdown is in the universe archive now, probably getting less or shorter support). Those articles also suggest editing the Linux kernel command line which seems like a rather massive impact. Does the kernel really need to know what userland tools will manage the network?

My environment is a server in a data centre used for shared web hosting and other services that has a static address, needs a few additional addresses and uses a VLAN to connect to other servers in the same data centre. It doesn't have any contact with WLAN. It may serve as a VPN server in some form.

On Ubuntu 18.04 both journald and rsyslog are installed. Both serve the same purpose of collecting log messages and storing them. So we have two programs doing the same work here.

What I could find out is that journald only saves log messages in its own journal files which can be queried with the journalctl command. No readable files are written. Also, journal will always collect log output from all the services that were started by systemd, which should always be all of them because ultimately systemd starts all processes even from older schemes like init scripts.

Rsyslog also receives log messages, through some socket that works like syslog has worked the past 50 years or so. Applications have to send their messages to that socket and rsyslog will receive them. Not sure how journald actually receives anything. Then rsyslog forwards these received messages into different readable files as per its configuration.

In Ubuntu, both are installed but do not seem to be connected. At least rsyslog does not load the "imjournal" module with which it could "read" log messages from journald. I don't understand how rsyslog (actively) reads anything, I thought it only (passively) receives messages. But it's not using that anyway.

The file /var/log/syslog contains largely the same content as shown by journalctl, just the output from sudo is missing in the file. But I haven't compared it all.

So how does this work? Who sends log messages to where and who receives them and where are they forwarded to? If both destinations are filled, does every application have to send messages to both syslog and journald separately? If they are interconnected, why are no messages duplicated? Are they filtered out again? Which location is more complete and where should I look if I want the complete picture?

If any of this has changed in newer versions of Ubuntu, I'd also be interested in that, as I'm going to switch an older server to 20.04 next year.

Edit: Here are some more resources on the topic:

• Interaction of Rsyslog and Journal (Red Hat sysadmin guide)
• imjournal (rsyslog documentation)
• rsyslog journal integration, Video presentation by the rsyslog author
• The syslog system call
• Coexistence with systemd (rsyslog documentation)

All of this information leaves me a bit confused. It seems like journal receives all syslog data from the system call in the first place (my /dev/log points to /run/systemd/journal/dev-log), and rsyslog fetches it from journal through a socket that looks like the socket that is had used before there was journal (possibly /run/systemd/journal/syslog, implicitly used if it sees systemd around). Then rsyslog can do all its advanced log processing (including writing the legacy /var/log files). If I don't need any of that magic, I might just disable rsyslog. But I'm not sure about that at all!

I'm setting up a new Ubuntu 18.04 server and have already played through one backup/restore loop. So the entire system has been restored from backup with a fresh RAID and LVM volumes.

Now recently, unattended-upgrades has reported this:

Processing triggers for initramfs-tools (0.130ubuntu3.8) ...
update-initramfs: Generating /boot/initrd.img-4.15.0-66-generic
I: The initramfs will attempt to resume from /dev/dm-1
I: (/dev/mapper/vg0-swap)
I: Set the RESUME variable to override this.

I tried to find out what that actually means but wasn't successful. What is it resuming there? Some process of generating boot files? I know it can take a while do do that. Does it have to do with the RAID? That is long finished with its resync. I don't get it. And what's actually wrong? What does that message want me to do? I'm clueless. If I don't need it, how can I make it go away?

The server did reboot successfully twice after that message so it can't be important. (If that "I" was supposed to mean something like that.)

Here's some commands if that helps:

> lvs
  LV   VG  Attr       LSize   Pool Origin Data%  Meta%  Move Log Cpy%Sync Convert
  root vg0 -wi-ao---- 400.00g
  swap vg0 -wi-ao----   8.00g

> cat /proc/mdstat
Personalities : [raid1] [linear] [multipath] [raid0] [raid6] [raid5] [raid4] [raid10]
md1 : active raid1 nvme1n1p2[0] nvme0n1p2[1]
      499449152 blocks super 1.2 [2/2] [UU]
      bitmap: 1/4 pages [4KB], 65536KB chunk

md0 : active raid1 nvme0n1p1[1] nvme1n1p1[0]
      523264 blocks super 1.2 [2/2] [UU]

unused devices: <none>

I can't find a good command to show something about these "dm-0" and "dm-1" devices that are also related to the RAID I guess.

I need to inspect and repair a Raspberry Pi SD card. This is my main goal. And it should be as simple as possible. It's already bad enough that Windows 10 cannot mount that file system and Android also has no idea about it (but creates random junk on the volume it understands). So I got an Ubuntu disk image and started the live system in VMware. I thought this should be the easiest and quickest solution to get to an environment that can handle a Linux file system.

I plugged in the card reader and it showed up as two volumes on the Ubuntu live desktop as expected. But the file I need to edit belongs to root. The default graphical text editor (it has no visible name) that is started from the default graphical file explorer (also has no visible name) only opens the file as read-only. Saving is not possible.

Smart Windows applications ask me for the required privileges when I want to use them. (Dumb Windows applications still don't.) I thought Linux apps were that smart before. But the editor isn't.

So what are my options to edit that file?

Is going to a terminal and using all the funny text UI tools all I can do now? I'd really prefer a GUI solution because I always forget terminal commands after not using them for a month. And the mount path seems to be unreadable for humans, it's so long I can't see it completely. I found the command gksudo nautilus somewhere around but it's not available on my system.

I have no idea where to look for this. Since the upgrade from Ubuntu Server 14.04 to 16.04 I consistently get every single e-mail from unattended-upgrade exactly twice. They have the same content and headers and even the same message ID but one is delivered some seconds later. Where can I find the reason for this? Has anybody seen this, too?

I'm using nano editor to edit my server's config files. Now I've discovered that pasting in a few lines removes all line breaks of the pasted lines as well as the following lines! It then says I can UnJustify that again. What?! Is this Microsoft Word auto formatting?

How can I prevent this from happening ever again?

UnJustify doesn't work, it only restores part of the broken text, not all.

This is Ubuntu Server 16.04.

How can I regularly delete certain files in cron?

I'm trying to delete empty files older than 15 minutes in the PHP sessions directory. I've tried several methods, all failed with different error messages.

4-59/10 *   * * *     root   [ -d /var/lib/php/sessions ] && find /var/lib/php/sessions/ -type f -cmin +15 -size 0c -print0 | xargs -n 200 -r -0 rm

xargs doesn't find 'rm'. It also won't find '/bin/rm'.

4-59/10 *   * * *     root   [ -d /var/lib/php/sessions ] && find /var/lib/php/sessions/ -type f -cmin +15 -size 0c -exec rm '{}'

Missing argument for -exec option.

4-59/10 *   * * *     root   [ -d /var/lib/php/sessions ] && find /var/lib/php/sessions/ -type f -cmin +15 -size 0c -delete

-delete option is unknown, find must be old.

Can Ubuntu 16.04 still do that? The first version mentioned worked fine on 14.04. Maybe I have to create a separate shell script file and simply write its name into the cron config if that's what cron can do. All the above commands work fine in an interactive bash shell (maybe except the last). Just not in cron.

My system monitoring program isn't working anymore since upgrading from Ubuntu Server 14.04 to 16.04 with MySQL 5.6 to 5.7. It performs the following command:

mysqladmin -u statuser extended-status

It also sets the MYSQL_PWD environment variable for that process to the required password. The error message however is:

mysqladmin: connect to server at 'localhost' failed
error: 'Access denied for user 'statuser'@'localhost' (using password: YES)'

When I try it interactively, it works fine:

mysqladmin -u statuser -p extended-status
(type in the password)

When I try to reproduce the tool's behaviour like this, it also fails:

MYSQL_PWD='********' mysqladmin -u statuser extended-status

So isn't MYSQL_PWD supported anymore? But it says "using password: YES" so it must have noticed my environment variable. It just doesn't seem to read it right.

I've set up unattended-upgrade on an Ubuntu 14.04.1 server. It has installed the kernel .41 over .40 yesterday at 4:10. Automatic reboot is configured for 3:00, so it should have rebooted last night. But it didn't.

Today, it installed another kernel version .43. Still the /var/run/reboot-required file does not exist, and the mail from unattended-upgrade doesn't contain any notice of a required reboot. So I don't expect the scheduled reboot to work tomorrow and the new kernel still won't be applied.

What's the issue here? Why doesn't that work as configured?

/etc/apt/apt.conf.d/20auto-upgrades:

APT::Periodic::Update-Package-Lists "1";
APT::Periodic::Unattended-Upgrade "1";

/etc/apt/apt.conf.d/50unattended-upgrades:

Unattended-Upgrade::Automatic-Reboot "true";
Unattended-Upgrade::Automatic-Reboot-Time "03:00";

I have added the following to my user's .bashrc file to get a longer prompt in less:

export LESS="-M"

This is added to the root user's .bashrc file as well, so when I sudo bash to get a root shell, it works just as well.

But when using sudo less …, it doesn't apply. There's only the simple colon prompt giving me no information at all where I am in the file. How can I change that?