Askerman's questions

I am using ubuntu 20.04 desktop and one day after booting up my PC, without me touching anything, the internet wasn't working. So after about an hour of frustration I found the magic commad that fixed the issue: sudo dhclient enp7s0

The problem is that now every time I reboot my computer, the interent doesn't work again, until I run this command. So for some reason the dhcp client isn't being started on boot anymore. What can I do to fix this issue?

I can probably set some sort of cronjob to run this command after boot, but that would be a terrible solution, as the networking manager should be able to start the dhcp client on its own.

I have the following script:

#!/bin/bash

echo "Merging pool...";

if !(mergerfs -o minfreespace=4G,defaults,allow_other,category.create=ff /media/pool/hdd1:/media/pool/hdd2:/media/pool/hdd4:/media/pool/hdd5 /media/pool/merged/)
then
        echo "Merging failed."
        exit 1;
fi

echo "Done";

exit 0;

It is saved in /home/me/scripts/mergePool.sh. If I manually run the script like this: sudo ./mergePool.sh, it works fine

I made this unit in /etc/systemd/system/mergePool.service:

[Unit]
Description=Merge all pool drives into one big virtual drive

[Service]
Type=oneshot
ExecStart=/bin/bash /home/me/scripts/mergePool.sh

[Install]
WantedBy=multi-user.target

If I run the unit like this:

sudo systemctl start mergePool.service

It produces no error and it doesn't work at all.

This is the log:

sudo systemctl status mergePool.service
● mergePool.service - Merge all pool drives into one big virtual drive
   Loaded: loaded (/etc/systemd/system/mergePool.service; enabled; vendor preset: enabled)
   Active: inactive (dead) since Sat 2020-02-29 12:26:07 CET; 6min ago
  Process: 2066 ExecStart=/bin/bash /home/me/scripts/mergePool.sh (code=exited, status=0/SUCCESS)
 Main PID: 2066 (code=exited, status=0/SUCCESS)

Feb 29 12:26:07 junkbox systemd[1]: Starting Merge all pool drives into one big virtual drive...
Feb 29 12:26:07 junkbox bash[2066]: Merging pool...
Feb 29 12:26:07 junkbox bash[2066]: Done
Feb 29 12:26:07 junkbox systemd[1]: Started Merge all pool drives into one big virtual drive.

This is quite confusing to me, why doesn't it work when the script is ran by systemd?

I want to permanently change MAC address of my network card on Ubuntu 18.04 LTS server, so I tried to follow some internet tutorials as well as similar answers on here, but they seem to all be for the older versions of Ubuntu.

The tutorials recommend changing the mac in /etc/network/interfaces, but when I open it it says:

# ifupdown has been replaced by netplan(5) on this system.  See
# /etc/netplan for current configuration.
# To re-enable ifupdown on this system, you can run:
#    sudo apt install ifupdown

But I found another file there called 50-cloud-init.yaml, which contains the following:

# This file is generated from information provided by
# the datasource.  Changes to it will not persist across an instance.
# To disable cloud-init's network configuration capabilities, write a file
# /etc/cloud/cloud.cfg.d/99-disable-network-config.cfg with the following:
# network: {config: disabled}
network:
    version: 2
    ethernets:
        eth0:
            dhcp4: true
            match:
                macaddress: b6:22:eb:7b:92:44
            set-name: eth0

At first I thought all I had to do was just edit the mac here, but it says on top that the changes won't be saved between reboots.

I found this command works:

sudo ip link set dev <your device here> address <your new mac address>

But it resets the mac back to the original after a reboot.

So how do I change the mac address for the eth0 permanently?

I have a bash script file where I execute a bunch of commands.

#!/bin/bash
umount /media/hdd1
umount /media/hdd2
something1
something2

But since the comands later in the file work with the umounted HDD, I need to make sure the umount is successful before continuing.

I can of course check if the umount failed and just exit 1, but that is not ideal.

So basically, what I would like to do, is somehow make the umount command wait, until the device is not busy and then umount the HDD and continue executing the script.

It would thus work like this:

#!/bin/bash
umount /media/hdd1 # Device umounted without any problems continuing the script..
umount /media/hdd2 # Device is busy! Let's just sit around and wait until it isn't... let's say 5 minutes later whatever was accessing that HDD isn't anymore and the umount umounts the HDD and the script continues
something1
something2

Thank you.

My system is split into two LVM partitions, one for / and one for /home. Before I install anything dangerous, I always create a snapshot of the / first.

I wanted some way to check the GPU temperature on my nvidia GPU and I found an upvoted answer on askubuntu recommending that I install nvidia-smi to achieve this feat. So I made the snapshot and then installed nvidia-smi. This turned out to be a big mistake, after rebooting, the login screen was in a small resolution and when I tried to log in I got a black screen and 5 seconds later was returned back to the login screen every time.

No big deal I thought, this is why I made the snapshot after all.

So I logged in over SSH which still worked, suggesting that only GUI was broken, and executed the merging command

lvconvert --merge /dev/main/systemSnapshot

The terminal replied that it can't do it right now, because the system is mounted and will do it on the next reboot. This is fine, I restored / snapshots like that several times before.

So I rebooted and was welcomed by the login screen in full resolution and everything seemed to be back in order, just as expected... that is until I tried to log in. Black screen... and then 5 seconds later thrown back onto the login screen as before.

How is this possible? The snapshot completely reversed the mess which nvidia-smi created, so how can it be still broken?

I thought that maybe the nvidia-smi created some nasty files in my home folder that were causing this, so I deleted most of the .dot files there but it had no effect.

So my question is, how is it possible that restoring the snapshot didn't fix the issue? I always felt safe knowing that I had a / snapshot running, which could easily undo any of my screw ups and now this feeling of safety was ripped away from me. I mean, snapshots are the only reason why I even use LVM.

I need to run a simple batch of commands after the computer boots, something like

sudo thing
sudo thing1 -p

But for the life of me I can't figure out how. I googled and googled and I kept finding the same thing: Place the commands into a /etc/rc.local or /etc/init.d/rc.local file. The problem is that none of those files exist on my system! Furthermore, I have read that /etc/rc.local is deprecated anyway, so what the correct and simple way to do this?

I would like to know how to these two things:

• run a command after the computer boots

• run a command after specified user logs in, and run it as the given user

  (And make all that happen solely by editing stuff in the terminal, no GUI tools)

Thank you.

I can move files with this command:

mv -t /mnt/hdd /home/me/movies/movie1.avi /home/me/movies/movie2.avi

The problem is, that it shows no progress at all, so I don't know if the operation is 1% done or 80% done.

I know that rsync is able to show progress.

So how would an rsync variation of that command above look like, while also showing the progress of the operation?

Thank you

I would like add a bunch of SATA HDDs into my HTPC and turn it into a NAS. The HTPC is running Ubuntu 16.04 LTS

To have a safety net for HDD failures, I will be using the SNAPraid with one parity HDD.

I want to create one big pool out of the HDDs, for ease of access and I also want to be able to easily add more HDDs later.

Since I will be using snapraid, then even though the HDDs will be pooled, I still need to be able to access them individually too (so the snapraid can function properly)

In addition to this, when I access the pool I don't really want all of the HDDs to spin up, since that would be a waste, only those whose files I will read or modify should spin up.

Is there any not too complicated piece of software for Ubuntu which can do these things?

Thanks

I have a directory, and I want all directories created in this directory, or its sub dirs, to be 777 and all files created in it or any of its subdirectories to be 666. It doesn't matter which user creates these files and dirs, I always want them to have those permissions by default.

I have tried to achive this with ACL but I am failing:

setfacl -R -d -m o::rw /home/test

For some reason, this makes the new files to be rw-r-r instead of rw-rw-rw.

Thank you for your advice

Up until now, I used Ubuntu 16 and everything worked fine. But then I did a clean install of Ubuntu 18 and now I am faced with a quite annoying problem.

Every time I turn on my computer, then during Ubuntu boot process the screen goes black, the computer does nothing, this continues 2 minutes, and then the PC continues to boot normally.

How can I fix this issue? I am using an HD5850 GPU with ubuntu drivers and have no extra hardware installed.

Here is the blame log

  1min 2.622s apt-daily-upgrade.service
         35.903s plymouth-quit-wait.service
         26.544s apt-daily.service
         15.870s dev-mapper-main\x2dsystem.device
         14.741s NetworkManager-wait-online.service
         13.610s dev-loop13.device
         13.574s dev-loop7.device
         13.504s dev-loop0.device
         13.493s dev-loop4.device
         13.480s dev-loop1.device
         13.448s dev-loop2.device
         13.384s dev-loop3.device
         13.357s dev-loop5.device
         13.351s dev-loop6.device
         13.334s dev-loop8.device
         13.320s dev-loop9.device
         13.286s dev-loop11.device
         13.257s dev-loop12.device
         13.206s dev-loop10.device
         12.549s snapd.service
         12.420s phpsessionclean.service
         12.400s plymouth-start.service
         10.951s networkd-dispatcher.service
lines 1-23...skipping...
     1min 2.622s apt-daily-upgrade.service
         35.903s plymouth-quit-wait.service
         26.544s apt-daily.service
         15.870s dev-mapper-main\x2dsystem.device
         14.741s NetworkManager-wait-online.service
         13.610s dev-loop13.device
         13.574s dev-loop7.device
         13.504s dev-loop0.device
         13.493s dev-loop4.device
         13.480s dev-loop1.device
         13.448s dev-loop2.device
         13.384s dev-loop3.device
         13.357s dev-loop5.device
         13.351s dev-loop6.device
         13.334s dev-loop8.device
         13.320s dev-loop9.device
         13.286s dev-loop11.device
         13.257s dev-loop12.device
         13.206s dev-loop10.device
         12.549s snapd.service
         12.420s phpsessionclean.service
         12.400s plymouth-start.service
         10.951s networkd-dispatcher.service

In Ubuntu 16, there was a hotkey option in the keyboard settings named something like "special key", which allowed me to type characters like <>{}

By default I have to type those characters by using the right alt.

In Ubuntu 18, this hotkey option is gone from the keyboard hotkeys, so how can I achieve this functionality now?

To put it more simply, instead of having to press Right "Alt + >" to type >, I want to press "left Alt + >" instead (or even more ideally "ctrl + left alt + >" if it is at all possible)

thank you

I am struggling with writing what I assume should be an easy script.

Basically I have a computer at work, which is hidden behind a NAT to which I don't have access. I need to SSH into this computer, so the only way to do this is to set a reverse port redirect, where this NATted computer will connect to my server at home, while redirecting a port for it self and then I can simply ssh into it through my home server.

The .sh script will be executed by the computer at work every 5 minutes and this is what I would like it to do:

Check if there is an active ssh connection to my server going on and if yes, then simply do nothing and exit the script.

If there is no active connection detected, then connect by executing "ssh [email protected] -i key.priv" and exit the script.

If the ssh connection attempt hangs for some reason, for say longer than 2 minutes, then force exit the script (not sure if this is possible to do, if not, then it doesn't have to be there)

Thank you kindly for your advice.

I have set default permissions for new files and groups in my directory like this

sudo setfacl -d -m g::rwX /<directory>

It works great. The problem is, that if I create any new files or directories in child directories of <directory>, the ACL I set no longer affects them. How can I make sure that the permissions above will also be applied to any new files or directory which are located anywhere under <directory>

I have been using SAMBA to share files on my HTPC and it worked fine until now. I haven't touched the HTPC in over a month and today the sharing suddenly stopped working by itself.

I traced the problem down to iptables. Currently I use this set of rules and up until now the samba worked flawlessly:

~$ sudo iptables -L -v
Chain INPUT (policy DROP 61 packets, 4786 bytes)
 pkts bytes target     prot opt in     out     source               destination
  102  6843 ACCEPT     all  --  any    any     anywhere             anywhere             state RELATED,ESTABLISHED
    0     0 ACCEPT     tcp  --  any    any     anywhere             anywhere             tcp dpt:ssh
    0     0 ACCEPT     udp  --  any    any     anywhere             anywhere             udp dpt:ssh
    0     0 ACCEPT     all  --  lo     any     anywhere             anywhere             /* This allows all traffic on localhost. */
    0     0 ACCEPT     udp  --  enp4s2 any     anywhere             anywhere             udp dpt:netbios-ns /* Samba LAN */
    0     0 ACCEPT     udp  --  enp4s2 any     anywhere             anywhere             udp dpt:netbios-dgm /* Samba LAN */
    0     0 ACCEPT     tcp  --  enp4s2 any     anywhere             anywhere             tcp dpt:netbios-ssn /* Samba LAN */
    0     0 ACCEPT     tcp  --  enp4s2 any     anywhere             anywhere             tcp dpt:microsoft-ds /* Samba LAN */
    0     0 ACCEPT     tcp  --  any    any     anywhere             anywhere             tcp dpt:http

Chain FORWARD (policy DROP 0 packets, 0 bytes)
 pkts bytes target     prot opt in     out     source               destination

Chain OUTPUT (policy ACCEPT 80 packets, 11372 bytes)
 pkts bytes target     prot opt in     out     source               destination

I have managed to get the samba working by changing Chain INPUT (policy DROP) to Chain INPUT (policy ACCEPT), but obviously this is just a temporary fix, since I don't want the htpc to just accept any suspicious incoming traffic.

Any idea why it stopped working all the sudden?

Thanks

I have a Canon Lide 120 scanner connected to my Ubuntu computer via standard USB.

To scan a document I have to open the scanner app, hit the scan, and then select a directory to save the image into. This is very time consuming, because I need to scan billions of pictures every day.

Is there any way to bind say a hotkey on my keyboard, or to rig a button on the scanner, so that if I press they hotkey or the scanner button, it will immediately scan the document inside of the scanner and save it into a directory, with no extra interaction needed?

Thanks

I configured my iptables like this:

Chain INPUT (policy DROP)
target     prot opt source               destination
ACCEPT     tcp  --  anywhere             anywhere             tcp dpt:ssh
ACCEPT     udp  --  anywhere             anywhere             udp dpt:ssh
ACCEPT     all  --  anywhere             anywhere //(this is loopback)

Chain FORWARD (policy DROP)
target     prot opt source               destination

Chain OUTPUT (policy ACCEPT)
target     prot opt source               destination

From my understanding, the browser should work fine, because the browser begins browsing through the OUTPUT, which is ACCEPTing everything, but it's not working. Where have I made a mistake?

And my second question is, when I added the loopback rule (iptables -A INPUT -i lo -j ACCEPT), it visually looks like a general rule that accepts traffic from anywhere and not just the loopback, which is pretty confusing, is there some way to tell it's a loopback rule if I don't know it is?

Thank you.

Up until now, I have been using a standard partitioning scheme for my Ubuntu installation:

- 4GB /swap
- 30GB /
- Rest of the HDD /home

However, I am reinstalling the Ubuntu now and would like to use snapshots and the other things which LVM offers.

The Ubuntu installer has a checkbox to install Ubuntu and set up LVM for it automatically, but I don't want to use this option, since I like to set up my partitions manually. That way, I can select things like the size of the swap partition, or size of the root partition and such, but alas, in the Ubuntu installer's manual partition tool, I don't see any option to create any LVM partition scheme or anything like that.

Is it possible to set up the LVM manually like that, or is the only option to let Ubuntu do it on full auto, by ticking that LVM box?

Thank you.

I recently installed Ubuntu server on my server to try out the linux as a new user. I followed a tutorial on how to set up the web server which said I need to chmod 777 the web server dir so that it can be written into.

Anyway, I created a new account for one dude to allow him to see some files on the server which I placed in his home dir:

adduser francis

After creating the account I checked what access he has with

groups francis

It said "francis : francis", so not a problem I thought, the ubuntu hasn't included him in any groups by default, which makes sense, it created him with no extra permissions security-wise, so everything is fine and dandy. A week later, in absolute and utter horror, I found out that even though he couldn't do things like SUDO or mess around in system directories, he had full access to almost everything else on the server. For example he had full read/write access to my web server files at /var/www (and thus passwords stored in php configs files etc) even though that directory is NOT in his home directory and I never added him into any groups which could access that directory, nor I granted him any special access to anything ever after doing the adduser.

Anyway, what is going on here? How do I kill his access to anything important? He should not be able to access stuff like /media or /var/www. I thought that new users were by default prevented from doing anything dangerous or snooping where they shouldn't be.

So the sum it up, I only need to allow him access to directories which I manually specify + to directories which he needs to function properly (his home dir, vim, nano etc..)

Thank you