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Old 08-21-2013, 08:44 PM   #1
gacanepa
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Registered: May 2012
Location: San Luis, Argentina
Distribution: Debian
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Filesystems supported by the kernel (/proc/filesystems)


Hi everyone,
From what I've read in plenty of places, everything seems to indicate that the /proc/filesystems file lists all the filesystems supported by the kernel currently in use. That is what I have read in this respectable site and in the RHEL 6 documentation.
Also, I have found 2 other threads in this very forum (1, 2) that deal with a similar question.
However, it is still not clear to me whether the /proc/filesystems file actualy lists all the filesystem types supported by the kernel currently in use, or if it only shows already loaded/present filesystem types.
I feel strongly about the second option, since this command
Code:
cat /proc/filesystems
did not include the iso9660 filesystem, and then I inserted a CD in my drive, ran the same command, and there it was, at the end of the list.
I looked up the config-3.5.0-17-generic inside /boot and I found these lines:
Code:
# CD-ROM/DVD Filesystems
#
CONFIG_ISO9660_FS=m
CONFIG_JOLIET=y
CONFIG_ZISOFS=y
CONFIG_UDF_FS=m
CONFIG_UDF_NLS=y
What does the "m" mean? (I assume "y" means "yes"). By the way, do these lines represent kernel modules by themselves?
Sorry for all the questions! But thanks in advance!
 
Old 08-21-2013, 08:52 PM   #2
astrogeek
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Quote:
Originally Posted by gacanepa View Post
Hi everyone,
From what I've read in plenty of places, everything seems to indicate that the /proc/filesystems file lists all the filesystems supported by the kernel currently in use. That is what I have read in this respectable site and in the RHEL 6 documentation.
Also, I have found 2 other threads in this very forum (1, 2) that deal with a similar question.
However, it is still not clear to me whether the /proc/filesystems file actualy lists all the filesystem types supported by the kernel currently in use, or if it only shows already loaded/present filesystem types.
I feel strongly about the second option, since this command
Code:
cat /proc/filesystems
did not include the iso9660 filesystem, and then I inserted a CD in my drive, ran the same command, and there it was, at the end of the list.
I looked up the config-3.5.0-17-generic inside /boot and I found these lines:
Code:
# CD-ROM/DVD Filesystems
#
CONFIG_ISO9660_FS=m
CONFIG_JOLIET=y
CONFIG_ZISOFS=y
CONFIG_UDF_FS=m
CONFIG_UDF_NLS=y
What does the "m" mean? (I assume "y" means "yes"). By the way, do these lines represent kernel modules by themselves?
Sorry for all the questions! But thanks in advance!
To answer your last question first, "m" means that it was compiled as a module, "y" means that it was compiled into the kernel, "n" means that it was not built.

To the first question, it is clear that it means "/proc/filesystems file lists all the filesystems supported by the kernel currently in use", and "currently in use" means just that - the kernel (and it's modules) currently in use.

So, since ISO9660 was built as a module, it is not "in the kernel" until the module is loaded, so the kernel currently in use does not support it until the module is loaded.

Hope that makes sense.
 
1 members found this post helpful.
Old 08-21-2013, 08:53 PM   #3
TobiSGD
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The file tells you all filesystems that are currently supported by the kernel. With putting in a CD you made the kernel load the iso9660 module, so that this was added to the list. I use a kernel with many filesystems inbuilt and /proc/filesystems shows up filesystems that were for sure never in use with this kernel.
Quote:
What does the "m" mean? (I assume "y" means "yes"). By the way, do these lines represent kernel modules by themselves?
These lines represent kernel options, some of them are options for specific drivers (the m tells the kernel to compile the iso9660 driver as a loadable module), some are options for the drivers (here the Joliet option, which is an extension to iso9660 and enabled), some are kernel options(for example the (in)famous PAE support option, not present in your example).
 
1 members found this post helpful.
Old 08-21-2013, 09:58 PM   #4
gacanepa
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Location: San Luis, Argentina
Distribution: Debian
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Thanks a lot astrogeek and TobiSGD. This is much clearer now. I already added to your reputation and will mark this thread as solved.
 
Old 08-22-2013, 07:57 AM   #5
gacanepa
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Location: San Luis, Argentina
Distribution: Debian
Posts: 182

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Hi again guys. Hope you don't mind another question related to this same thing.
Let's suppose that after inserting a CD or a DVD in the drive, the iso9660 filesystem module is not loaded automatically by the kernel and therefore it's not visible in the /proc/filesystems file.
In the man page for modprobe, I found the following:
Quote:
modprobe intelligently adds or removes a module from the Linux kernel: note that for convenience, there is no difference
between _ and - in module names (automatic underscore conversion is performed). modprobe looks in the module directory
/lib/modules/`uname -r` for all the modules and other files...
Then I checked the /lib/modules/3.2.0-4-686-pae directory and found and modules.alias file, and found out that isofs is an alias for the isso9660 module.
So the question is, say the iso9660 module is not loaded automatically by the kernel as I said before, am I correct in assuming that
Code:
modprobe -a isofs
inserts the module into the running kernel?
At least, that's what the result of my test seems to indicate . I'll copy here the /proc/filesystems file before and after the test:
BEFORE:
Code:
root@debian:/lib/modules/3.2.0-4-686-pae# cat /proc/filesystems
nodev   sysfs
nodev   rootfs
nodev   bdev
nodev   proc
nodev   cgroup
nodev   cpuset
nodev   tmpfs
nodev   devtmpfs
nodev   debugfs
nodev   securityfs
nodev   sockfs
nodev   pipefs
nodev   anon_inodefs
nodev   devpts
nodev   ramfs
nodev   hugetlbfs
nodev   pstore
nodev   mqueue
nodev   usbfs
        ext3
nodev   rpc_pipefs
nodev   nfs
nodev   nfs4
nodev   nfsd
root@debian:/lib/modules/3.2.0-4-686-pae#
AFTER (modprobe -a isofs):
Code:
root@debian:/lib/modules/3.2.0-4-686-pae# cat /proc/filesystems
nodev   sysfs
nodev   rootfs
nodev   bdev
nodev   proc
nodev   cgroup
nodev   cpuset
nodev   tmpfs
nodev   devtmpfs
nodev   debugfs
nodev   securityfs
nodev   sockfs
nodev   pipefs
nodev   anon_inodefs
nodev   devpts
nodev   ramfs
nodev   hugetlbfs
nodev   pstore
nodev   mqueue
nodev   usbfs
        ext3
nodev   rpc_pipefs
nodev   nfs
nodev   nfs4
nodev   nfsd
        iso9660
root@debian:/lib/modules/3.2.0-4-686-pae#
Then after removing the iso9660 module (modprobe -r isofs):
Code:
root@debian:/lib/modules/3.2.0-4-686-pae# cat /proc/filesystems
nodev   sysfs
nodev   rootfs
nodev   bdev
nodev   proc
nodev   cgroup
nodev   cpuset
nodev   tmpfs
nodev   devtmpfs
nodev   debugfs
nodev   securityfs
nodev   sockfs
nodev   pipefs
nodev   anon_inodefs
nodev   devpts
nodev   ramfs
nodev   hugetlbfs
nodev   pstore
nodev   mqueue
nodev   usbfs
        ext3
nodev   rpc_pipefs
nodev   nfs
nodev   nfs4
nodev   nfsd
root@debian:/lib/modules/3.2.0-4-686-pae#
 
Old 08-22-2013, 02:15 PM   #6
astrogeek
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Yes that is correct as I read your post.
 
  


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