I have a laptop running Ubuntu 18.04 which is paired with an external Bluetooth speaker. It takes me seven mouse clicks to connect to this speaker (such as when the laptop has been outside range of the speaker).
Is there a way to connect to a USB device in fewer steps than this?
In Ubuntu 18.04 when a workspace has no more windows it is automatically removed and the workspaces which were over and under the removed workspace become adjacent.
Is there any way to perform the reverse of that?
I have two adjacent workspaces which both have multiple windows, and I would like to move a window from one of these workspaces to a new workspace between the two existing workspaces.
I was surprised to see this error message in Chromium on Ubuntu 18.04 when trying to view an image in a post on a StackExchange site:
This site can’t be reached
i.stack.imgur.com’s server IP address could not be found.
DNS_PROBE_FINISHED_NXDOMAIN
In an attempt to find out what was happening I tried to run tcpdump to look at the DNS requests and responses. I attempted to reload the image giving me the error and this was the DNS traffic that I saw:
# tcpdump -pni any 'port 53'
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on any, link-type LINUX_SLL (Linux cooked), capture size 262144 bytes
20:10:17.618041 IP 127.0.0.1.42714 > 127.0.0.53.53: 3068+ A? i.stack.imgur.com. (35)
20:10:17.618080 IP 127.0.0.1.42714 > 127.0.0.53.53: 23569+ AAAA? i.stack.imgur.com. (35)
20:10:17.618861 IP 127.0.0.53.53 > 127.0.0.1.42714: 3068 13/0/0 CNAME i.stack.imgur.com.cdn.cloudflare.net., A 104.16.0.35, A 104.16.26.34, A 104.16.2.35, A 104.16.30.34, A 104.16.28.34, A 104.16.24.34, A 104.16.25.34, A 104.16.29.34, A 104.16.27.34, A 104.16.3.35, A 104.16.1.35, A 104.16.31.34 (277)
20:10:17.619395 IP 127.0.0.53.53 > 127.0.0.1.42714: 23569| 16/0/0 CNAME i.stack.imgur.com.cdn.cloudflare.net., AAAA 2001:67c:2b0:db32:0:1:6810:1f22, AAAA 2001:67c:2b0:db32:0:1:6810:1b22, AAAA 64:ff9b::6810:23, AAAA 2001:67c:2b0:db32:0:1:6810:223, AAAA 2001:67c:27e4:64::6810:123, AAAA 64:ff9b::6810:1f22, AAAA 2001:67c:27e4:64::6810:1f22, AAAA 2001:67c:27e4:64::6810:223, AAAA 2001:67c:27e4:64::6810:1b22, AAAA 2001:67c:27e4:64::6810:1922, AAAA 2001:67c:2b0:db32:0:1:6810:1d22, AAAA 64:ff9b::6810:123, AAAA 2001:67c:2b0:db32:0:1:6810:1e22, AAAA 64:ff9b::6810:1822, AAAA 2001:67c:2b0:db32:0:1:6810:1822 (505)
As you can see the DNS resolution succeeded. But Chromium was still showing me the same NXDOMAIN error message. What could cause Chromium to report NXDOMAIN when the lookups were indeed successful?
I have an IPv6-only network where I am now trying to add a NAT64 gateway. The NAT64 is not on my default gateway because it's intended to use a different ISP than the default gateway.
The default gateway is advertised using radvd and IPv6 connection is working. However the NAT64 provided by the ISP is unreliable and thus I want to configure my own NAT64.
On the machine where my NAT64 is running I have created this radvd configuration:
interface enp4s0
{
AdvSendAdvert on;
AdvDefaultPreference low;
route 64:ff9b::/96 {
AdvRoutePreference high;
};
};
But it is not working. On the client machines I only see the default route and not the 64:ff9b::/96 route to the NAT64 gateway.
I have a network running IPv6 connected to the internet through a router running Ubuntu Server 14.04. My laptop running Ubuntu 14.04 can connect to this network using either Ethernet or WiFi which both work as intended.
Occasionally the laptop is connected to other networks where I would like it to still use the IP address it has from its home network. Mobility Support in IPv6 as defined in RFC 6275 (formerly RFC 3775) sounds like the way to achieve that.
Is that protocol supported by Ubuntu?
I have used apt-cache search to look for packages mentioning mobility or either RFC number, but found nothing relevant. And I have searched this site as well and found no earlier questions about IPv6 mobility support.
I have an Ubuntu 16.04 machine connected to an IPv6 only network. One application I want to run on this machine appears to not work properly with IPv6.
I know 464XLAT is supposed to make such applications work. The NAT64 part is operated by the ISP and is working as intended. However there is no CLAT on the Ubuntu machine, which is where I am stuck now.
Does Ubuntu support CLAT? And how do I enable it?
I have a computer running Ubuntu 16.04. I would like to make voice calls between this computer and another computer also running Ubuntu 16.04.
Both of the computers have IPv6 (one of them has a static IP address). Both of them have IPv4 access through NAT (NAT64 on one of the computers and NAT444 on the other).
Can I make a voice call directly between the two computers without relying on third party services?
Any software available in the standard Ubuntu 16.04 repositories can be installed on both computers if necessary.
In 14.04 I could close a meld window by pressing Ctrlq. But in 16.04 the behavior of that key combination has changed to terminate all currently open invocations of meld rather than just the one I pressed the key combination in.
I also tried Ctrlw, but that can only close individual tabs and the window remains open even if all tabs inside it have been closed.
Is there a keyboard combination which will close a single meld window in 16.04?
When viewing files in meld I sometimes need to copy the path of a file. In 14.04 and earlier the file names were shown as text fields where I could easily copy the path from.
In 16.04 the text field has been replaced with a widget used for loading a file. So I can no longer copy the path like I used to.
How can I copy the path of a file I am viewing in meld in 16.04?
I am trying to configure VirtualBox on Ubuntu Server 14.04. But when I try to start a VM I get an error message saying:
VT-x is disabled in the BIOS.
Searching for this error message lead me to multiple pages suggesting to reboot the machine and change the settings in the BIOS. Unfortunately at the moment I only have ssh access to this server. Through ssh I can reboot the machine, but I don't know how to change the BIOS settings.
Is there any other way to get a virtual machine running on this server which I can only access through ssh? I tried disabling VT-x in VirtualBox but am told that is not a valid configuration when using a 64-bit guest.
I have an Ubuntu Server 14.04 install which is connected to the internet using PPPoE. At the moment my ppp0 interface have an MTU of 1492 which mostly works.
I'd like to increase the MTU to 1500, which is supported by my ISP.
So far I have increased the MTU of the underlying Ethernet interface to 1508, and I have tried adding the following lines in /etc/ppp/peers/dsl-provider
mtu 1500
mru 1500
But my ppp0 interface still has an MTU of 1492. I believe the syntax of my added lines is correct, since using values lower than 1492 does work as expected.
Manually changing the MTU of the ppp0 interface to 1500 after it has been brought up works, but it only affects packets in one direction. Doing that I am able to send 1500 bytes packets across the internet and they will arrive at their destination with no fragmentation. But incoming traffic to me is still sent in 1492 byte fragments.
By capturing traffic on the Ethernet interface as the PPPoE connection is brought up, I can see that in the configuration request that my Ubuntu Server 14.04 machine sends to the provider, the MRU is specified as 1492. So I know the issue is on my end of the connection.
Why does Ubuntu Server 14.04 use 1492 as MRU in the configuration request, when the configuration file says 1500? And how can I change it to 1500?
I am trying to install Ubuntu Server 14.04 and am currently stuck on this error:
INFO: Menu item 'apt-setup-udeb' succeeded but requested to be left unconfigured.
At that point the installer stops. I am presented a menu where I can choose which step of the install to execute next. If choose to install GRUB and then reboot I can boot and log in. But I don't have all the software I wanted, and apt won't install any additional software.
What might be the reason apt-setup-udeb won't be configured during install?
My search for explanations lead me to some very old Debian bug reports which did not help me understand the problem and one deleted question which I cannot read.
On Ubuntu Server 14.04 when I type a command not currently installed, it will tell me which packages I can choose from to install. Here is an example of what that looks like:
# chromium-browser
The program 'chromium-browser' is currently not installed. You can install it by typing:
apt-get install chromium-browser
This feature was enabled by default. I didn't have to do anything myself to get such suggestions. Now if I do the same on a fresh install of Ubuntu Server 16.04, it looks like this:
# chromium-browser
bash: chromium-browser: command not found
What do I need to do on Ubuntu Server 16.04 to get the behavior I am used to from 14.04?
(In the above examples I used chromium-browser because it is a package I knew I hadn't installed on any of my servers. But it could be any package not installed by default.)
I am using 14.04 on an AMD64 compatible system. Inside this system I am trying to run a virtual machine also with 14.04. I start qemu with this command:
qemu-system-x86_64 -cdrom ubuntu-14.04.3-desktop-amd64.iso -m 2048
Ubuntu boots inside qemu. But as soon as I move the mouse inside the qemu window, the cursor turns invisible. I can click on items just inside the border of the virtual screen, and this works so I know the mouse emulation is sort of working.
However since the cursor is invisible I have no idea where I am clicking when I try to click on something close to the center of the virtual screen.
What do I need to do to make the mouse cursor visible in qemu?
I am trying to boot a Ubuntu 14.04 live system on a machine that is currently unable to boot from its harddisk due to the installed OS having gotten corrupted somehow.
I used this command to write the install image to the USB device
# cat /var/tmp/ubuntu-14.04.1-desktop-i386.iso >/dev/sdb
When trying to boot, I got an error message saying isolinux.bin missing or corrupt. Nothing else was output to the screen during boot.
Afterwards I verified the integrity of the USB media again like this:
# head -c1034944512 /dev/sdb | sha256sum
5cd41b34c86799c92d316718d9763d225847bbc290aba0dc312623418e02d6cf -
This appears to be the correct checksum, so I have no reason to think the image is corrupted. What else could be the reason for this error message?
I have an SSD that I want to TRIM before installing Ubuntu on it. It has been suggested to me, that I leave some unpartitioned space, such that the wear leveling will have free blocks to work with. However I understand that because the drive has previously had some software installed, just repartitioning it with some space left unpartitioned is insufficient. And mkfs won't TRIM the unpartitioned area.
In reading the hdparm man page, I came across --trim-sector-ranges, which sounds exactly what I need to use. It also has a warning which says: EXCEPTIONALLY DANGEROUS. DO NOT USE THIS OPTION!! twice.
I have seen a recomendation suggesting to use the ATA secure erase command instead. But I also read that secure erase has the risk of bricking the device.
What is it that --trim-sector-ranges does that makes it so dangerous that it is better to run the risk of bricking the device?
I have Ubuntu 14.04 running on a Dell Latitude 13 laptop. When I launch Chromium and open several pages from stackexchange in different tabs. Any text I type in will frequently have characters showing up in a different order from how they were typed. For example, this paragraph actually showed up as:
I have Ubuntu 14.04 runnign on aDell Latitude 1 3laptop. Whne I alucnh Chormium na dopne several pages form tsackexchnag ei ndiffreent tabs. Any text I type in will ferwuqently have cahracters shwoing up in adifferent ofrdre form hwo htye weer ytped. For exmapel, thsi apragraph actually shwoed up as
As you can imagine having to manually fix that every time it happens can be very frustrating. The behavior looks as if some layer in the software stack is inserting key presses into a stack rather than a queue, and if they are not consumed as quickly as they arrive, they show up in the wrong order.
This only happens sporadically, and seems to happen more often when Chromium is swapping a lot. I have not been able to identify which layer of the software stack is causing the problem. Is there any additional debugging/logging I could enable to show me in which order characters show up at different layers in the software stack?
What I have tried so far
By sending alternating STOP and CONT signals to an xterm, I was able to slow down xterm just enough to reproduce the symptom. Since reordering of keyboard input is not supposed to happen even if xterm is frozen for a little bit, I think it is safe to conclude that the flaw is not in Chromium or stackexchange, but rather in some software being involved in both cases.
In order to rule out the possibility that it may be a flaw in the keyboard hardware, I tested with synthetic key presses.
sleep 10 ; for K in {a..z} ; do xdotool type "$K" ; sleep 0.2 ; done
With that command I was able to reproduce the problem. On one occasion the keys showed up in the order abcdefghlmkjpnioqrstuvwxyz. So when it also happens with keypresses generated by xdotool, it cannot be a flaw in the keyboard or keyboard controller.
If I speed up the input produced using xdotool even further, it causes the xterm to lock up.
Seeing an xterm lock up when keyboard input arrives quickly is something I have seen even without artificially slowing it down using STOP signals. When I do see xterm lock up like that, it usually keeps happening after I kill the xterm and start a new one. That problem persists until I run compiz --replace. After running that command everything runs faster and xterm no longer locks up at least for the first few days.
So there is some evidence suggesting that the two problems are related and somehow has something to do with compiz, but I don't have any solid evidence to back up that suspicion.
On a fresh install of Ubuntu 14.04, I get this error message during boot
the disk drive for /dev/mapper/cryptswap1 is not ready yet or not present
and the swap partition is never activated. From my searches so far I have found:
Is it possible to use encrypted swap on Ubuntu 14.04 without using this sort of hack? I am perfectly comfortable updating all the installed packages and fix those configuration files, which got initialized with incorrect content due to buggy install scripts. I'd rather avoid having to use my own script to activate swap, as that sort of approach have a tendency to break when packages are updated.
This is what my /etc/crypttab looks like:
cryptswap1 /dev/sda6 /dev/urandom swap,cipher=aes-cbc-essiv:sha256,offset=16
And the relevant line from my /etc/fstab is:
/dev/mapper/cryptswap1 none swap sw 0 0
What I have tried so far:
I have found message disk drive for /dev/mapper/cryptswap1 is not ready yet or not present even after trying various options asking about what might be the same scenario.
But the only answer is suggesting to using un-encrypted swap.
I have found http://ubuntuforums.org/showthread.php?t=2200995 which claims to have a solution, but the solution makes no sense to me.
The first part of the proposed solution is to rewrite the encrypted swap header using mkswap. However since this header is encrypted with a key, that is not persistent across reboots, this step wouldn't help getting the swap working after the next reboot.
It also suggests updates to /etc/fstab, but it appears my fstab is already looking correctly.
The post assumes LVM, which I do not use. I am unaware of any way, that would make a difference.
I have found https://bugs.launchpad.net/ubuntu/+source/ecryptfs-utils/+bug/1310058 which helped me understand the issue with the swap header being overwritten and that adding offset to crypttab and regenerating the unencrypted swap header, can resolve this problem.
However the overwritten header is not the only issue at play, there is another issue, which I do not fully understand yet.
Other things I have found out about the problem:
From reading /lib/cryptsetup/cryptdisks.functions I learned that during boot, the device is supposed to be created using the name cryptswap1_unformatted then the encrypted swap header is to be written, and the device is to be renamed as cryptswap1. In the kernel log I find this error message:
[ 39.419429] device-mapper: ioctl: Unable to change name on mapped device cryptswap1_unformatted to one that already exists: cryptswap1
Confusingly the outcome of that turns out to be that the device does end up having the name cryptswap1, but the swap header never got written.
Swap works during those boots where a file system check was performed. It is only when no file system checks is performed, that I get the dreaded cryptswap1 is not ready yet error.
In /var/log/upstart/cryptdisks.log I find the error message
Device cryptswap1_unformatted already exists.
However by adding some additional logging to /lib/cryptsetup/cryptdisks.functions, I learned that there is a race between /etc/init.d/cryptdisks-early and /etc/init/cryptdisks.conf. Any logging I add to cryptdisks.functions can influence how the actions of the two scripts are interleaved, and occasionally, it ends up working.
It is clear that the two are not supposed to be handling the same device in parallel. How can I get the two scripts serialized, such that swap works on every boot?
In Ubuntu 12.04 I can use the tcpdump command to see network packets in real time. A typical invocation could look like this: tcpdump -pni eth0
In Ubuntu 14.04 the exact same command no longer displays packets in real time. When I run the command nothing happens for the first second. After a second it prints out all the packets transferred during the last second and then stops again.
Having packets in the packet capture show up out of order compared to other output I am looking at makes it harder to debug networking problems.
Is there any way I can get tcpdump to behave like it used to and display the packets as soon as they are transferred instead of waiting up to a second each time?
No, I cannot use WireShark as I have to debug machines that are on the Internet, not on the same LAN.
I want to add a feature to pam, and I figured a good starting point was to download the libpam-modules source. On download, I notice this warning: gpgv: Can't check signature: public key not found
What is the official method for verifying the integrity of source packages, when apt-get cannot find the public key?
The newest version of ubuntu-keyring and debian-keyring packages are installed already.
There are ways to find the corresponding public key and install it. However that in itself does not provide integrity, because in effect it is trusting the contents of the dsc file to tell me which public key to use to verify the signature on the dsc file.
Is the gpg signature on the dsc file a critical part of the integrity verification? Could a man in the middle or a rouge mirror serve a malicious version of the file where the warning from gpg is the only indication something bad is happening? Or does apt-get have other means of validating the integrity?
Where would I find official documentation on the security model? Ideally I would like to understand the full trust path from the install image to the source package I am downloading.
The full output from the download was this:
$ apt-get source libpam-modules
Reading package lists... Done
Building dependency tree
Reading state information... Done
Picking 'pam' as source package instead of 'libpam-modules'
NOTICE: 'pam' packaging is maintained in the 'Bzr' version control system at:
https://code.launchpad.net/~ubuntu-core-dev/pam/ubuntu
Please use:
bzr branch https://code.launchpad.net/~ubuntu-core-dev/pam/ubuntu
to retrieve the latest (possibly unreleased) updates to the package.
Need to get 2,043 kB of source archives.
Get:1 http://dk.archive.ubuntu.com/ubuntu/ trusty/main pam 1.1.8-1ubuntu2 (dsc) [2,510 B]
Get:2 http://dk.archive.ubuntu.com/ubuntu/ trusty/main pam 1.1.8-1ubuntu2 (tar) [1,893 kB]
Get:3 http://dk.archive.ubuntu.com/ubuntu/ trusty/main pam 1.1.8-1ubuntu2 (diff) [147 kB]
Fetched 2,043 kB in 6s (316 kB/s)
gpgv: Signature made Fri 31 Jan 2014 11:12:23 PM CET using RSA key ID 64792D67
gpgv: Can't check signature: public key not found
dpkg-source: warning: failed to verify signature on ./pam_1.1.8-1ubuntu2.dsc