I have a volume mounted at /media.
I have an additional volume mounted at /media/dvd.
I have mounted things this way as I understand that minidlna can only use a single directory for, say, videos.
Each volume is structured with sub directories. On the main director, /media everything works, the folder structure works, and adding new files appear automatically.
I cannot get minidlna to recognise the /media/dvd directory. I have tried to restart, force-reload, and even deleted the files.db file to force a refresh.
I don’t know whether the issue is:
The fact that I have one mount point inside another
The permissions need fixing
The fact that the second volume /media/dvd is HFS+; the volume mounts well enough and I can read & write from the shell (touch test).
Something else … ?
I am running Centos 6.
Related
I've mostly worked in Windows environments and am still very noobish in everything Linux, so it's very likely I'm missing basic Linux concepts. That being said, I have questions about logical volumes and their interactions with files :
I have to use an Ubuntu machine (which I did not set up). On this machine, there is a physical volume /dev/sda2 which is in a volume group vg0.
That volume group vg0 has 4 logical volumes : lv1, mounted on /, lv2, mounted on /boot, lv3, mounted on /var and lv4, mounted on /tmp
My questions are as follows :
If I save a file (for example foo.txt) in the /var directory, will it be stored on the lv3(/var) logical volume ?
If the lv3(/var) logical volume is full and I try to save foo.txt in the /var directory, will it be stored on the lv1(/) logical volume (after all, /var is in /) ?
If the lv1(/) volume is full and I try to save foo.txt somewhere outside of /var (for example in /home), will it be stored on the lv3(/var) logical volume ?
What could be the point of having all these logical volumes, would 1 volume on / not be much simpler ?
It's quite obvious, from my questions, that I don't really get the relations between logical volumes, mount points and files. Is there somewhere a good tutorial where I could educate myself ?
Thanks in advance.
Yes, because lv3 is mounted on /var any files put in /var go there.
No, there are no special cases that happen when the device is full - you just get a device is full error. Despite /var appearing to be a child of /, that has been overridden by mounting lv3 on /var
No, again because there are no special cases for the device being full. It doesn't care, it just tries to put the file where it goes.
Yes, it is much simpler to have it all in /. But it can cause problems. For example, /boot is often its own volume so that you can't fill it up and prevent your system from working if you download a bunch of stuff in your home folder. There are different schools of thought on how much/how little you should separate your file system into different volumes. It is somewhat just opinion, but those opinions are based on various use cases and problems.
I don't have a great answer other than use the search engine of your choice! Honestly, when you are starting out it doesn't matter so much as long as you have space to put your stuff! If you are a newbie, it might be good to just put everything in one volume - as long as you keep an eye and don't let it fill up.
I've got quite a head scratcher here. We have multiple Raspberry Pis on the field hundreds of kilometers apart. We need to be able to safe(ish)ly upgrade them remotely, as the price for local access can cost up to few hundred euros.
The raspis run rasbian, / is on SD-card mounted in RO to prevent corruption when power is cut (usually once/day). The SD cards are cloned from same base image, but contain manually installed packages and modified files that might differ between devices. The raspis all have a USB flash as a more corruption resistant RW-drive and a script to format it on boot in case the drive is corrupted. They call home via GPRS connection with varying reliability.
The requirements for the system are as follows:
Easy versioning of config files, scripts and binaries, at leasts /etc, /root and home preferably Git
Efficient up-/downgrade from any verion to other over GPRS -> transfer file deltas only
Possibility to automatically roll back recently applied patch, if connection is no longer working
Root file system cannot be in RW mode while downloading changes, the changes need to be stored locally before applying to /
The simple approach might be keeping a complete copy of the file system in a remote git repository, generate a diff file between commits, upload the patch to the field and apply it. However, at the the moment the files on different raspis are not identical. This means, at least when installing the system, the files would have to be synchronized through something similar to rsync -a.
The procedure should be along the lines of "save diff between / and ssh folder to a file on the USB stick, mount / RW, apply diff from file, mount / RO". Rsync does the diff-getting and applying simultaneously, so my first question becomes:
1 Does there exist something like rsync that can save the file deltas from local and remote and apply them later?
Also, I have never made a system like this and the drawt is "closest to legit I can come up with". There's a lot of moving parts here and I'm terrified that something I didn't think of beforehand will cause things to go horribly wrong. Rest of my questions are:
Am I way off base here and is there actually a smarter/safe(r) way to do this?
If not, what kind of best practices should I follow and what kind of things to be extremely careful with (to not brick the devices)?
How do I handle things like installing new programs? Bypass packet manager, install in /opt?
How to manage permissions/owners (root+1 user for application logic)? Just run everything as root and hope for the best?
Yes, this is a very broad question. This will not be a direct answer to your questions, but rather provide guidelines for your research.
One means to prevent file system corruption is use an overlay file system (e.g., AUFS, UnionFS) where the root file system is mounted read-only and a tmpfs (RAM based) or flash based read-write is mount "over" the read-only root. This requires your own init scripts including use of the pivot_root command. Since nothing critical is mounted RW, the system robustly handles power outages. The gist is before the pivot_root, the FS looks like
/ read-only root (typically flash)
/rw tmpfs overlay
/aufs AUFS union overlay of /rw over /
after the pivot_root
/ Union overlay (was /aufs
/flash read only root (was /)
Updates to the /flash file system are done by remounting it read-write, doing the update, and remounting read-only. For example,
mount -oremount,rw <flash-device> /flash
cp -p new-some-script /flash/etc/some-script
mount -oremount,ro <flash-device> /flash
You may or may not immediately see the change reflected in /etc depending upon what is in the tmpfs overlay.
You may find yourself making heavy use of the chroot command especially if you decide to use a package manager. A quick sample
mount -t proc none /flash/proc
mount -t sysfs none /flash/sys
mount -o bind /dev /flash/dev
mount -o bind /dev/pts /flash/dev/pts
mount -o bind /rw /flash/rw #
mount -oremount,rw <flash-device> /flash
chroot /flash
# do commands here to install packages, etc
exit # chroot environment
mount -oremount,ro <flash-device> /flash
Learn to use the patch command. There are binary patch commands How do I create binary patches?.
For super recovery when all goes wrong, you need hardware support with watchdog timers and the ability to do fail-safe boot from alternate (secondary) root file system.
Expect to spend significant amount of time and money if you want a bullet-proof product. There are no shortcuts.
I'm trying to build a new filesystem with deduplication using FUSE.
I tried running the fusexmp_fh.c provided in the example section of the FUSE. However after mounting the filesystem at a mount point, I can see all the existing directories inside the mount point. I dont need those directories. I want the mounted filesystem to be empty.
I tried searching through fusexmp_fh.c but could not find out where the existing directories get added.
Can someone explain to me how this works?
Also
can fusexmp_fh.c be taken as a base for building the filesystem?
Does it have all the basic functionalities?
Are you saying that you mounted the file system over a non-empty directory, and you can see the previous contents of the directory? (In which case, the answer is "don't mount to a non-empty mount point". Usually it throws an error to tell you not to do that.)
If what you're seeing is the directories and files in the directory that you are using as your base directory, that's the normal behavior for a loopback file system, which is what fusexmp_fh.c is. The example file system takes a mount point, and passes all commands on that mount point through to a backing directory. If you use a backing directory that has files in it, you will now see those files in two places, the original location and the mounted fuse directory.
If you want to understand how the directory filling works, start by taking a look at readdir, and see how the stat items that it returns are constructed. Each of those is a single directory entry.
Yes, you can use fusexmp_fh.c as the basis for a basic file system, it's got all the necessary pieces, although extended metadata isn't supported. (But adding it is fairly trivial for a loopback.)
I understand that a file system can be visualized as a "tree" of files and directories. I also understand that "mounting" a file system means to placing or rooting that tree within an existing directory. https://askubuntu.com/questions/20680/what-does-it-mean-to-mount-something
With that said, I have mounted an implementation of python fuse that is similar to this one. When I run my implementation, it runs to the end of the init method and then just shows a blinking cursor. So fuse is getting mounted. I know that fuse is mounted because of what happens when I run $mount
$mount
...
FuseHandler on /home/memsql/mount
So now that I've mounted fuse, how do I access the files.
The linked tutorial says
You will see all files in /your/dir under /mnt/point and be able to
manipulate them exactly as if they were in the original filesystem.
How exactly do you do this? Can somebody show me, syntactically, how to instantiate and query Fuse? How do you perform a read or write? What does code that performs those operations look like?
As l4mpi notes, you’ve now mounted a file system, so it will respond to the standard Unix file system API, and FUSE will handle the file system operations. You can cd to it, ls in it, read or creat files in it, etc.
I used the following linx command :
mv RegisteredOutputs.msg registered_outputs.tcl
My intention was to achieve the following :
mv RegisteredOutputs.msg registered_outputs.msg
The directory in which I issued the command already had a file named registered_outputs.tcl .
So by far you might have figured out what my issue is. registered_outputs.tcl got overwritten. Is there any way of recovering it ?
First thing you always do: Boot a live CD/USB so that your partition is mounted read-only, to avoid those spaces on the drive being re-used. Once another file uses that platter space, the data is gone.
Because of how Linux ext3 file system works, it actually zeroes out inode data on delete, making recovery impossible. This is for delete however, and I don't know if the same could apply to overwriting existing files. Hope you're feeling lucky.
See this guide on how to recover deleted files on ext3
source:
recovery of overwritten file