Nagabhushan S N's questions

I recently learned that Ubuntu uses disk cache / filesystem cache (size is displayed in system monitor). I couldn't see any documentation that says there is a default limit on how much RAM can be used for disk cache. So, I assumed that disk cache size can grow till it completely consumes RAM.

However, I noticed something that says otherwise. I'm training a deep neural network with a large dataset. On one machine with 32GB RAM, disk cache grows till 27GB (rest other applications are using 3-4 GB and hence, around 1GB of RAM is still free). Because of this disk caching, the subsequent training epochs are much faster. But on another machine with 64GB RAM, disk cache grows only till 18GB (same dataset, same program, more than 30GB RAM is still free). Because of this, it is not able to cache the entire dataset and hence my subsequent training epochs are not benefitting from this disk caching.

I don't understand why the second machine is not using the additional RAM to cache the entire dataset. The only reason I can think of is that there is a limit set on how much RAM can be used for disk cache on the second machine, but not on the first machine. Is this true? If so, how can I increase this limit?

Idk if this matters, the first machine has Ubuntu 18.04 and the second one has Ubuntu 20.04.

PS: I searched on this site, unix.stackexchange, stackoverflow and google, but couldn't find anything (may be I'm not using the right keywords?)

I have Ubuntu 18.04 (dual boot with Windows 10). Headphones work properly in Windows 10. In Ubuntu, if the headphones are connected before starting ubuntu, it works fine. But if I remove the headphone and then connect them again, no sound comes in the headphone, though, I can see the output device in settings.

I have tried multiple solutions in this and other forums (like the ones described here). Most of the questions say headphones not working. But my problem is slightly different. They work after rebooting the machine. But if I unplug them and plug them again, they won't work. I have to restart the machine again.

Is there any solution to fix this problem? Is it possible to reinstall drivers, if that may help? I can provide any extra information, if needed

I had installed notepad++ using Softwares in my Ubuntu 18.04, which installed notepad++ using snap. Now, for some reason, my notepad++ is not opening. But I want to get all the unsaved text files I had opened in my previous session. Where can I find these unsaved files?

Most of the questions on web deal with Windows, but not for ubuntu. They usually say that the files are saved in a folder named backup. I searched in the home directory, snap directory. I couldn't find any folder named backup.

I have an external hard disk which was formatted as ext4. I recently connected this HDD to a new system and all of a sudden, the format changed to exFat. I have no idea how this happened. Is it possible to convert exFat back to ext4?

I have a lot of symlinks in the HDD. But exFat doesn't support symlinks. This is causing a huge problem for me. Is there any way out?

The outputs of various commands are below

$ df -Th
Filesystem     Type      Size  Used Avail Use% Mounted on
/dev/sdb2      fuseblk   3.7T  2.8T  905G  76% /media/smart/BackupPlus

$ fsck -N /dev/sdb2
fsck from util-linux 2.34
[/sbin/fsck.ext2 (1) -- /dev/sdb2] fsck.ext2 /dev/sdb2

$ lsblk -f
NAME        FSTYPE   LABEL      UUID                                 FSAVAIL FSUSE% MOUNTPOINT
sdb                                                                                 
├─sdb1      vfat     EFI        67E3-17ED                                           
└─sdb2      exfat    BackupPlus 5FA8-BCEE                             904.5G    76% /media/smart/BackupPlus

$ mount | grep sdb2
/dev/sdb2 on /media/smart/BackupPlus type fuseblk (rw,nosuid,nodev,relatime,user_id=0,group_id=0,default_permissions,allow_other,blksize=4096,uhelper=udisks2)

$ blkid /dev/sdb2
/dev/sdb2: LABEL="BackupPlus" UUID="5FA8-BCEE" TYPE="exfat" PARTUUID="ff2c7cdb-a161-4ee2-8c52-2eba4c63b23b"

$ sudo file -sL /dev/sdb2
/dev/sdb2: DOS/MBR boot sector

$ cat /etc/fstab
# /etc/fstab: static file system information.
#
# Use 'blkid' to print the universally unique identifier for a
# device; this may be used with UUID= as a more robust way to name devices
# that works even if disks are added and removed. See fstab(5).
#
# <file system> <mount point>   <type>  <options>       <dump>  <pass>
# / was on /dev/nvme0n1p2 during installation
UUID=8bb8cb68-d702-47e1-9ed1-791f8746830f /               ext4    errors=remount-ro 0       1
# /boot/efi was on /dev/nvme0n1p1 during installation
UUID=E5DA-F3CE  /boot/efi       vfat    umask=0077      0       1
/swapfile                                 none            swap    sw              0       0

I'm using Space File Manager instead of Nautilus. Yesterday my laptop became non-responsive and hence I did a hard restart (hold down power button for 5-10 seconds). After restart, all my bookmarks and settings in Space File Manager are gone! Is there any way to recover the bookmarks? If not, is there at least a way to backup the bookmarks and settings so that if it repeats again, I can restore them.

I'm accessing my lab PC from my laptop from home. I'm using either TeamViewer or Anydesk to access the remote computer. But since last few days, after a restart of remote computer, I'm not able to access the remote PC properly. In the sense, I am able to connect via TeamViewer or Anydesk. After connecting via TeamViewer, I can see the login screen of the remote PC. After I enter the system password, it logs me in and then everything freezes. The favorites on the dock are also not shown. Only TeamViewer and Anydesk windows are open and they are unresponsive too. At this point, someone has to physically restart the PC. In order for me to access the remote PC properly, someone has to physically be present at the PC and login (after restart). Is this a known problem? Is it possible to rectify this?

More details: We don't have UPS backup in lab and so whenever there is a power cut, PC shuts down. I've configured the PC to start automatically on AC power. Earlier, once it starts, I was able to login using TeamViewer or AnyDesk. But since few days, this new problem arose.

I'm using Space File Manager in my Ubuntu 18.04 as a substitute for Nautilus File Manager. But SpaceFM doesn't have an option to move deleted files to trash. Instead it deletes them permanently. I followed this answer to add a new command that moves selected files to trash when pressing delete.

However, if I want to restore after deleting, neither ctrl+Z works nor going to trash and right click and select restore (no restore option). How can I get this functionality in Space FM? i.e. to restore files when pressing ctrl+Z and right click within trash and select restore.

I've dual-booted my laptop with Windows 10 and Ubuntu 18.04. While installing Ubuntu, I created a swap space of 15GB. My laptop has 8GB RAM. I hadn't noticed earlier, but now that my system is running out of memory, I noticed that System Monitor shows only 1.1GB swap. Turning off swap and turning it on doesn't help either. What is happening here? How can I fix it?

PS: I don't know if it matters. Initially I had tried to disable swap altogether. I followed this answer and set swappiness to 10. Now I've changed it back to the default value 60.

Edit1:
Adding content of /etc/fstab

$ cat /etc/fstab
# /etc/fstab: static file system information.
#
# Use 'blkid' to print the universally unique identifier for a
# device; this may be used with UUID= as a more robust way to name devices
# that works even if disks are added and removed. See fstab(5).
#
# <file system> <mount point>   <type>  <options>       <dump>  <pass>
# / was on /dev/nvme0n1p7 during installation
UUID=3f9f3cd3-acfb-47a8-aff2-fac6a7405e02 /               ext4    errors=remount-ro 0       1
# /boot/efi was on /dev/nvme0n1p1 during installation
UUID=B827-57AB  /boot/efi       vfat    umask=0077      0       1
/swapfile                                 none            swap    sw              0       0
# (identifier)  (location, eg sda5)   (format, eg ext3 or ext4)      (some settings) 
UUID=3a70fe9d-3ffc-4e4e-b7b1-d94f2dbe0bbd   /home    ext4          defaults       0       2 

In Ubuntu 18.04, I'm not able to dock TeamViewer. Even if I right click on the TeamViewer icon when opened, I can't see an option to make it favorite. How can I dock the teamviewer here permanently?

I'm following this guide to install miktex in my Ubuntu 18.04. However, I want to install it in a custom location (~/Softwares/MikTex). Is it possible to do this? If yes how?

The reason I need to do this is because, in my laptop root has only 25GB and I've less than 10GB left. I don't want to use it up. However, home has around 250GB.

I'm trying to dual boot my Dell G3 system that came with pre-installed windows 10. When I disabled secure boot, I couldn't even load into windows saying bitlocker encryption. I then had to find my key and input it. Then I was able to boot into windows. But when I tried installing ubuntu, I can't find my disk at all - I can only see the installation medium. Changing SATA from RAID to AHCI as said here also didn't help.

When using multiple tabs in nautilus file explorer in ubuntu, by default it shows the opened folder name in the tab name. Is it possible to rename that to a fixed name per tab?

I'm trying to install ubuntu in dual boot along with windows 10. I have two hard disks. Windows is already installed in disk0. Then I installed ubuntu 18.04 LTS in disk0 after windows. Both were working fine. But every time I restart, it used to load windows by default. To enable grub, I found the below command and executed in windows command prompt with administrator privilages

bcdedit /set {bootmgr} path \EFI\ubuntu\grubx64.efi

After this, whenever I reboot, it opens Grub command line. If I go to bios/uefi, I can start ubuntu from there or I can select Windows Boot Manager. Ubuntu is working fine, but if I select Windows Boot Manager, again I get into Grub command line. So, I'm not able to boot windows at all.

How to fix this? I found a command to undo bcdedit

bcdedit /deletevalue {bootmgr} path \EFI\ubuntu\grubx64.efi

But to execute this, I need to be in windows right? So, I'm not able to execute this command. Is there a way to perform this action from bios/uefi (Asus computer) or from the ubuntu? (Ubuntu is booting fine)

Or is there any other method? I'm open to all suggestions.

Additional Info: Also, I installed grub2 and now I'm able to see grub bootloader after restart. Here, I get 2 options: ubuntu and windows (from sda2). If I select Ubuntu, ubuntu loads fine. But if I select windows, I get an error saying invalid signature

Edit 01: I ran boot-repair tool. The details are in this paste ubuntu