[Samsung Gear S3] adfree:
sh-3.2# mount /dev/dm-0 -o remount,rw
mount: cannot remount /dev/mapper/rootfs read-write, is write-protected

sh-3.2# mount /dev/mapper/rootfs -o remount,rw
mount: cannot remount /dev/mapper/rootfs read-write, is write-protected

:rolleyes:

https://unix.stackexchange.com/questions/351327/what-are-these-dm-devices

sh-3.2# findmnt /
TARGET SOURCE FSTYPE OPTIONS
/ /dev/mapper/rootfs ext4 ro,relatime,data=ordered

sh-3.2# ls -l /dev/mapper/rootfs
brw-rw---- 1 root disk 253, 0 Sep 8 06:49 /dev/mapper/rootfs

sh-3.2# cat /sys/class/block/dm-0/dm/name
rootfs

sh-3.2# lsblk
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
loop0 7:0 0 13.6M 1 loop /usr/share/locale
loop1 7:1 0 320K 1 loop /opt/share/zoneinfo
zram0 254:0 0 279.3M 0 disk [SWAP]
mmcblk0rpmb 179:24 0 512K 0 disk
mmcblk0boot0 179:8 0 4M 1 disk
mmcblk0boot1 179:16 0 4M 1 disk
mmcblk0 179:0 0 3.7G 0 disk
|-mmcblk0p1 179:1 0 32M 0 part
|-mmcblk0p2 179:2 0 8M 0 part /csa
|-mmcblk0p3 179:3 0 2M 0 part
|-mmcblk0p4 179:4 0 20M 0 part
|-mmcblk0p5 179:5 0 8M 0 part
|-mmcblk0p6 179:6 0 8M 0 part
|-mmcblk0p7 179:7 0 3M 0 part
|-mmcblk0p8 259:0 0 16M 0 part
|-mmcblk0p9 259:1 0 16M 0 part
|-mmcblk0p10 259:2 0 16M 0 part /usr/lib/modules
|-mmcblk0p11 259:3 0 190M 0 part /opt/system/csc
|-mmcblk0p12 259:4 0 158M 0 part /opt
|-mmcblk0p13 259:5 0 1.9G 0 part /opt/usr
|-mmcblk0p14 259:6 0 1.3G 0 part
| `-rootfs 253:0 0 1.2G 1 crypt /
`-mmcblk0p15 259:7 0 256K 0 part

sh-3.2# mount | grep root
/dev/mapper/rootfs on / type ext4 (ro,relatime,data=ordered)

:confused:

Best Regards

Edit 1.

Google search...

https://en.wikipedia.org/wiki/Device_mapper

https://en.wikipedia.org/wiki/Dm-crypt

sh-3.2# cryptsetup --help
cryptsetup 1.6.7
Usage: cryptsetup [OPTION...] <action> <action-specific>
--version Print package version
-v, --verbose Shows more detailed error messages
--debug Show debug messages
-c, --cipher=STRING The cipher used to encrypt the disk
(see /proc/crypto)
-h, --hash=STRING The hash used to create the encryption
key from the passphrase
-y, --verify-passphrase Verifies the passphrase by asking for
it twice
-d, --key-file=STRING Read the key from a file.
--master-key-file=STRING Read the volume (master) key from file.
--dump-master-key Dump volume (master) key instead of
keyslots info.
-s, --key-size=BITS The size of the encryption key
-l, --keyfile-size=bytes Limits the read from keyfile
--keyfile-offset=bytes Number of bytes to skip in keyfile
--new-keyfile-size=bytes Limits the read from newly added
keyfile
--new-keyfile-offset=bytes Number of bytes to skip in newly added
keyfile
-S, --key-slot=INT Slot number for new key (default is
first free)
-b, --size=SECTORS The size of the device
-o, --offset=SECTORS The start offset in the backend device
-p, --skip=SECTORS How many sectors of the encrypted data
to skip at the beginning
-r, --readonly Create a readonly mapping
-i, --iter-time=msecs PBKDF2 iteration time for LUKS (in ms)
-q, --batch-mode Do not ask for confirmation
-t, --timeout=secs Timeout for interactive passphrase
prompt (in seconds)
-T, --tries=INT How often the input of the passphrase
can be retried
--align-payload=SECTORS Align payload at <n> sector boundaries
- for luksFormat
--header-backup-file=STRING File with LUKS header and keyslots
backup.
--use-random Use /dev/random for generating volume
key.
--use-urandom Use /dev/urandom for generating volume
key.
--shared Share device with another
non-overlapping crypt segment.
--uuid=STRING UUID for device to use.
--allow-discards Allow discards (aka TRIM) requests for
device.
--header=STRING Device or file with separated LUKS
header.
--test-passphrase Do not activate device, just check
passphrase.
--tcrypt-hidden Use hidden header (hidden TCRYPT
device).
--tcrypt-system Device is system TCRYPT drive (with
bootloader).
--tcrypt-backup Use backup (secondary) TCRYPT header.
--veracrypt Scan also for VeraCrypt compatible
device.
-M, --type=STRING Type of device metadata: luks, plain,
loopaes, tcrypt.
--force-password Disable password quality check (if
enabled).
--perf-same_cpu_crypt Use dm-crypt same_cpu_crypt
performance compatibility option.
--perf-submit_from_crypt_cpus Use dm-crypt submit_from_crypt_cpus
performance compatibility option.

Help options:
-?, --help Show this help message
--usage Display brief usage

<action> is one of:
open <device> [--type <type>] [<name>] - open device as mapping <name>
close <name> - close device (remove mapping)
resize <name> - resize active device
status <name> - show device status
benchmark <name> - benchmark cipher
repair <device> - try to repair on-disk metadata
erase <device> - erase all keyslots (remove encryption key)
luksFormat <device> [<new key file>] - formats a LUKS device
luksAddKey <device> [<new key file>] - add key to LUKS device
luksRemoveKey <device> [<key file>] - removes supplied key or key file from LUKS device
luksChangeKey <device> [<key file>] - changes supplied key or key file of LUKS device
luksKillSlot <device> <key slot> - wipes key with number <key slot> from LUKS device
luksUUID <device> - print UUID of LUKS device
isLuks <device> - tests <device> for LUKS partition header
luksDump <device> - dump LUKS partition information
tcryptDump <device> - dump TCRYPT device information
luksSuspend <device> - Suspend LUKS device and wipe key (all IOs are frozen).
luksResume <device> - Resume suspended LUKS device.
luksHeaderBackup <device> - Backup LUKS device header and keyslots
luksHeaderRestore <device> - Restore LUKS device header and keyslots

You can also use old <action> syntax aliases:
open: create (plainOpen), luksOpen, loopaesOpen, tcryptOpen
close: remove (plainClose), luksClose, loopaesClose, tcryptClose

<name> is the device to create under /dev/mapper
<device> is the encrypted device
<key slot> is the LUKS key slot number to modify
<key file> optional key file for the new key for luksAddKey action

Default compiled-in key and passphrase parameters:
Maximum keyfile size: 8192kB, Maximum interactive passphrase length 512 (characters)
Default PBKDF2 iteration time for LUKS: 1000 (ms)

Default compiled-in device cipher parameters:
loop-AES: aes, Key 256 bits
plain: aes-cbc-essiv:sha256, Key: 256 bits, Password hashing: ripemd160
LUKS1: aes-xts-plain64, Key: 256 bits, LUKS header hashing: sha1, RNG: /dev/urandom