1

I have to mount a old USB key formatted with FAT filesystem. The mount must be executed automatically by a udev rule which executes a bash script.

When the USB key is inserted in the USB port, the script, for now, executes the command:

blkid -o udev /dev/sda1

where /dev/sda1 is the partition present inside the USB and formatted with FAT32 (or FAT16) filesystem. The output of the previous command for the USB key is empty.

The output of the same command (blkid) for other USB keys contains the udev variable ID_FS_TYPE; possible values of ID_FS_TYPE are: vfat, ntfs, exfat.
So an empty output for the execution of blkid happens only for this old USB and I'm not able to know why it happens only for it.

Different options for mount command if the filesystem is vfat

If the value of the variable ID_FS_TYPE is vfat the script must execute the following mount command:

> mount -o rw,relatime,users,gid=100,umask=000,shortname=mixed,utf8=1,flush /dev/sda1 /mount/point

While if the filesystem is not vfat the options for the mount command can be the following:

mount -o rw,relatime /dev/sda1 /mount/point

With the particular USB key (1 GB and very old) the script by the command blkid, can't determine that the filesystem type is vfat so it executes the second mount command; the result is that the permissions for the mount point directory (called /media/sda1) are:

> ls -l /media/ total 16 drwxr-xr-x 3 root root 16384 Jan 1 1970 sda1

while I need:

# ls -l /media/ total 16 drwxrwxrwx 3 root root 16384 Jan 1 1970 sda1

I need those permissions because all users must be able to write on the USB and not only the proprietary (that is root in my context).

Find file system type by other commands

This link gives other tips to get the filesystem type of this particular USB key. So I have tried other commands:

  • lsblk -n -o FSTYPE /dev/sda1: also in this case, for my specific USB key, the output of the command is empty
  • the output of the command file -sL /dev/sda1 instead is very long; I show this output below:
> file -sL /dev/sda1 /dev/sda1: DOS/MBR boot sector, code offset 0x3c+2, OEM-ID "MSDOS5.0", sectors/cluster 32, reserved sectors 8, root entries 512, Media descriptor 0xf8, sectors/FAT 240, sectors/track 63, heads 255, hidden sectors 2048, sectors 1966080 (volumes > 32 MB), reserved 0x1, serial number 0xa4906b9d, unlabeled, FAT (16 bit)

In this output it is present the info FAT (16 bit), but it is not clear that the filesystem of the partition of the USB key is formatted vfat. If I execute the previous file -sL command on a USB key formatted by NTFS filesystem the output of the command is:

> file -sL /dev/sda /dev/sda: DOS/MBR boot sector, code offset 0x52+2, OEM-ID "NTFS ", sectors/cluster 8, Media descriptor 0xf8, sectors/track 63, heads 255, dos < 4.0 BootSector (0x0), FAT (1Y bit by descriptor); NTFS, sectors/track 63, physical drive 0x80, sectors 15654911, $MFT start cluster 786432, $MFTMirror start cluster 2, bytes/RecordSegment 2^(-1*246), clusters/index block 1, serial number 030fcd5a9fcd56a1c; contains bootstrap BOOTMGR

In this output is present the string NTFS, but is present also the string FAT, so with this output it is not easy to establish that the filesystem is vfat and not ntfs.

The question

Is there a command other than the previous ones that can provide the filesystem of an USB key before mounting it?

Improve this question
2
  • This question is similar to: How can I determine the fs type of my current working directory?. If you believe it’s different, please edit the question, make it clear how it’s different and/or how the answers on that question are not helpful for your problem. Commented Apr 22 at 13:39
  • @thecarpy In my case the USB key is not mount I need to know its filesystem to mount it correctly.. The post which you have linked to this question is not useful. Commented Apr 22 at 13:48

3 Answers 3

Reset to default
3

You could use vol_id which should be able to detect the file system, it is designed to be used in udev:

vol_id -t /dev/sda1

Note that depending on the size of the partition, some tools create FAT16 instead of FAT32 partitions when you format to FAT. BTW, vFAT supports both FAT16 and FAT32.

Update following comment:

An alternative to vol_id can be lshw:

lshw -class disk

man lshw

mans vol_id

Improve this answer
2
  • Thanks, but on my systems I don't have the command vol_id. I'm triyng on a Mint distribution and on an embedded linux distribution. Commented Apr 22 at 14:10
  • Thanks, but the command sudo lshw -class disk on my system doesn't give any information about the (strange) USB inserted. Commented Apr 23 at 8:46
3

lsblk -f .... I can't imagine a modern distro not having lsblk installed.

Improve this answer
1
  • Thanks. In the question I have written that the command lsblk is present and if I use the command: lsblk -n -o FSTYPE /dev/sda1 for only the problematic old USB the output is empty. For other USB it returns the correct filesystem type. Commented Apr 23 at 6:47
1

By this answer, and some other adjustments, I have found the solution at this strange problem.

The only command which gives information about the filesystem type of the partition present on my USB is file -s /dev/sda1 command; so I must use it to recover the filesystem type.

I have modified my script in this way:

# Get info for this drive: $ID_FS_LABEL, $ID_FS_UUID, and $ID_FS_TYPE eval $(/sbin/blkid -o udev ${DEVICE}) # Global mount options OPTS="rw,relatime" if [[ -z ${ID_FS_TYPE} ]]; then file_output=$(file -s ${DEVICE}); if echo "$file_output" | grep -q "FAT (32 bit)"; then echo "Is FAT32" ID_FS_TYPE="vfat" elif echo "$file_output" | grep -q "FAT (16 bit)"; then echo "Is FAT16" ID_FS_TYPE="vfat" else echo "I don't know what this thing is" fi fi # File system type specific mount options if [[ ${ID_FS_TYPE} == "vfat" ]]; then OPTS+=",users,gid=100,umask=000,shortname=mixed,utf8=1,flush" fi if ! /bin/mount -o ${OPTS} ${DEVICE} ${MOUNT_POINT}; then echo "Error mounting ${DEVICE} (status = $?)" /bin/rmdir ${MOUNT_POINT} exit 1 fi

In the script:

  • the value of the DEVICE variable is /dev/sdX (for example /dev/sda1)
  • the command eval $(/sbin/blkid -o udev ${DEVICE}) tries getting the filesystem type into the udev variable ID_FS_TYPE
  • the value of the MOUNT_POINT variable is the mount point on my filesystem

In this way the old USB key formatted by FAT32 (or by FAT16) is mounted automatically by the script and all users of my system can write on it.

Improve this answer

You must log in to answer this question.

Start asking to get answers

Find the answer to your question by asking.

Ask question

Explore related questions

See similar questions with these tags.