Write protected error when mounting a loop device with a GPT and single partition

I'm trying to mount a loop device that I've created with the following steps but receive an error telling me that the fs is of an unknown type. If I don't add a partition to the fs it will mount as expected.
- $ sudo dd if=/dev/zero of=secOps bs=1M count=512
- 512+0 records in
- 512+0 records out
- 536870912 bytes (537 MB) copied, 0.244399 s, 2.2 GB/s
- $ sudo mkfs.ext4 secOps
- mke2fs 1.42.9 (28-Dec-2013)
- secOps is not a block special device.
- Proceed anyway? (y,n) y
- Discarding device blocks: done
- Filesystem label=
- OS type: Linux
- Block size=4096 (log=2)
- Fragment size=4096 (log=2)
- Stride=0 blocks, Stripe width=0 blocks
- 32768 inodes, 131072 blocks
- 6553 blocks (5.00%) reserved for the super user
- First data block=0
- Maximum filesystem blocks=134217728
- 4 block groups
- 32768 blocks per group, 32768 fragments per group
- 8192 inodes per group
- Superblock backups stored on blocks:
- 32768, 98304
- Allocating group tables: done
- Writing inode tables: done
- Creating journal (4096 blocks): done
- Writing superblocks and filesystem accounting information: done
- $ sudo gdisk secOps
- GPT fdisk (gdisk) version 0.8.10
- Partition table scan:
- MBR: not present
- BSD: not present
- APM: not present
- GPT: not present
- Creating new GPT entries.
- Command (? for help): o
- This option deletes all partitions and creates a new protective MBR.
- Proceed? (Y/N): Y
- Command (? for help): n
- Partition number (1-128, default 1):
- First sector (34-1048542, default = 2048) or {+-}size{KMGTP}:
- Last sector (2048-1048542, default = 1048542) or {+-}size{KMGTP}: +256M
- Current type is 'Linux filesystem'
- Hex code or GUID (L to show codes, Enter = 8300):
- Changed type of partition to 'Linux filesystem'
- Command (? for help): p
- Disk secOps: 1048576 sectors, 512.0 MiB
- Logical sector size: 512 bytes
- Disk identifier (GUID): 941146DD-99DB-4A90-B400-8D7D1534AF21
- Partition table holds up to 128 entries
- First usable sector is 34, last usable sector is 1048542
- Partitions will be aligned on 2048-sector boundaries
- Total free space is 524221 sectors (256.0 MiB)
- Number Start (sector) End (sector) Size Code Name
- 1 2048 526335 256.0 MiB 8300 Linux filesystem
- Command (? for help): w
- Final checks complete. About to write GPT data. THIS WILL OVERWRITE EXISTING
- PARTITIONS!!
- Do you want to proceed? (Y/N): Y
- OK; writing new GUID partition table (GPT) to secOps.
- Warning: The kernel is still using the old partition table.
- The new table will be used at the next reboot.
- The operation has completed successfully.
- $ sudo losetup /dev/loop0 secOps
- $ sudo lsblk
- NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
- sda 8:0 0 20G 0 disk
- ├─sda1 8:1 0 200M 0 part /boot/efi
- └─sda2 8:2 0 19.8G 0 part /
- loop0 7:0 0 512M 0 loop
- └─loop0p1 259:0 0 256M 0 loop
- $ sudo blkid
- /dev/sda1: SEC_TYPE="msdos" UUID="8939-51F5" TYPE="vfat" PARTLABEL="EFI System Partition" PARTUUID="c8b5c89a-17ed-480e-b9f6-0e811c16fee3"
- /dev/sda2: LABEL="root" UUID="a8ee4848-df7a-4cc9-a9f0-07e423353d28" TYPE="xfs" PARTUUID="e8d78e3d-29f6-44f1-bd31-977ffd4b3d7d"
- /dev/loop0: PTTYPE="gpt"
- /dev/loop0p1: PARTLABEL="Linux filesystem" PARTUUID="b0ad9144-89bf-49ce-9038-f70d9d69d7ea"
I notice here that the partition does not have a UUID. Why might that be?
And then when attempting to mount the loop device.
- $ sudo mount /dev/loop0 /secOpsMnt/
- mount: /dev/loop0 is write-protected, mounting read-only
- mount: unknown filesystem type '(null)'
Comments
-
Hi @GRO 108 , I have the following questions:
1.- What OS and version are you working with?
2.- Did you do "losetup -f" before using /dev/loop0 ? "losetup -f" gives the first available loop device. And it's probably you are messing something up if /dev/loop0 was busy. This is how it looks on Ubuntu 20.04:
luis@ubuntu20:~$ sudo losetup -f
/dev/loop9==> That means I could start working with /dev/loop9, not anything below that.
So, just to check on it:
luis@ubuntu20:~$ ls -l /dev/loop*
brw-rw---- 1 root disk 7, 0 Kun 19 18:25 /dev/loop0
brw-rw---- 1 root disk 7, 1 Kun 19 18:25 /dev/loop1
brw-rw---- 1 root disk 7, 2 Kun 19 18:25 /dev/loop2
brw-rw---- 1 root disk 7, 3 Kun 19 18:25 /dev/loop3
brw-rw---- 1 root disk 7, 4 Kun 19 18:25 /dev/loop4
brw-rw---- 1 root disk 7, 5 Kun 19 18:26 /dev/loop5
brw-rw---- 1 root disk 7, 6 Kun 19 18:26 /dev/loop6
brw-rw---- 1 root disk 7, 7 Kun 19 18:26 /dev/loop7
brw-rw---- 1 root disk 7, 8 Kun 19 18:26 /dev/loop8
brw-rw---- 1 root disk 7, 9 Kun 19 19:12 /dev/loop9
crw-rw---- 1 root disk 10, 237 Kun 19 18:25 /dev/loop-controlAnd lsblk shows that /dev/loop0 is being used:
luis@ubuntu20:~$ lsblk
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
loop0 7:0 0 49,8M 1 loop /snap/snap-store/433
loop1 7:1 0 27,1M 1 loop /snap/snapd/7264
loop2 7:2 0 55M 1 loop /snap/core18/1705
loop3 7:3 0 62,1M 1 loop /snap/gtk-common-themes/1506
loop4 7:4 0 240,8M 1 loop /snap/gnome-3-34-1804/24
loop5 7:5 0 29,9M 1 loop /snap/snapd/8542
loop6 7:6 0 55M 1 loop /snap/core18/1880
loop7 7:7 0 49,8M 1 loop /snap/snap-store/467
loop8 7:8 0 255,6M 1 loop /snap/gnome-3-34-1804/36
sda 8:0 0 15G 0 disk
├─sda1 8:1 0 512M 0 part /boot/efi
├─sda2 8:2 0 1K 0 part
└─sda5 8:5 0 14,5G 0 part /
sr0 11:0 1 57,7M 0 rom /media/luis/VBox_GAs_6.1.10So, please unmont the device and start again.
Many regards,
Luis.0 -
- CentOS 7 - kernel version 3.10.0-1127.10.1.el7.x86_64
- I did know previous to running these steps that the
/dev/loop0
device was free
I was able to mount the loop-device with a fs attached but no GPT or partition. After running
gdisk
and adding those it wasn't possible to mount it.0 -
I will try to repeate your steps later, but please note you did mkfs.ext4 on the file, sec04fs or whatever you called it, then you tried to moutnt dev/loop0 after you wiped out the entire disk with gpart as it said it did. So why should there be a fs there now? A quick glance tells me the mkfs.ext4 was discarded. It would certainly be the case if you did say "mkfs.ext4 /dev/sde ; then ran fdisk to set up partitions on sde ; and then tried to mount any of them, include /dev/sde1 .
1
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