Не могу записать таблицу разделов

#!/bin/sh
for ((sector=16100; sector<=17000 ; sector++)) 
do
   offset=$(($sector*512))
   cmd="mount -t ntfs-3g /dev/sda /mnt/tmp/ -o ro,offset=$offset"
   echo "sector: $sector offset: $offset";
   $cmd 2>/dev/null && echo "partition found @ offset $offset!" && break
done

fdisk -l /dev/sda

Disk /dev/sda: 465.8 GiB, 500107862016 bytes, 976773168 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x5e9ea2f8

Устр-во   Загрузочный     Start Конец    Blocks  Id System
/dev/sda1                 16065 976768064 488376000   f W95 Ext'd (LBA)
/dev/sda5                 16128 976768064 488375968+  7 HPFS/NTFS/exFAT

./script.sh
sector: 16100 offset: 8243200
sector: 16101 offset: 8243712
sector: 16102 offset: 8244224
sector: 16103 offset: 8244736
sector: 16104 offset: 8245248
sector: 16105 offset: 8245760
sector: 16106 offset: 8246272
sector: 16107 offset: 8246784
sector: 16108 offset: 8247296
sector: 16109 offset: 8247808
sector: 16110 offset: 8248320
sector: 16111 offset: 8248832
sector: 16112 offset: 8249344
sector: 16113 offset: 8249856
sector: 16114 offset: 8250368
sector: 16115 offset: 8250880
sector: 16116 offset: 8251392
sector: 16117 offset: 8251904
sector: 16118 offset: 8252416
sector: 16119 offset: 8252928
sector: 16120 offset: 8253440
sector: 16121 offset: 8253952
sector: 16122 offset: 8254464
sector: 16123 offset: 8254976
sector: 16124 offset: 8255488
sector: 16125 offset: 8256000
sector: 16126 offset: 8256512
sector: 16127 offset: 8257024
sector: 16128 offset: 8257536
partition found @ offset 8257536!

mount | grep sda
/dev/sda on /mnt/tmp type fuseblk (ro,nosuid,nodev,allow_other,blksize=4096)

losetup -a
/dev/loop0: [2101]:13 (/mnt/usr/usr.sq)
/dev/loop1: [2103]:22 (/mnt/opt/opt.sq)
/dev/loop2: [2101]:14 (/mnt/usr/src.sq)
/dev/loop3: [2101]:11 (/mnt/usr/portage.sq)
/dev/loop5: [0005]:7210 (/dev/sda), offset 8257536

=== START OF INFORMATION SECTION ===
Device Model:     LITEONIT LCS-256L9S-11 2.5 7mm 256GB
Serial Number:    TW03YYV3550854A16201
Firmware Version: HC8110B
User Capacity:    256,060,514,304 bytes [256 GB]
Sector Size:      512 bytes logical/physical
Rotation Rate:    Solid State Device
Device is:        Not in smartctl database [for details use: -P showall]
ATA Version is:   ATA8-ACS, ATA/ATAPI-7 T13/1532D revision 4a
SATA Version is:  SATA 3.1, 6.0 Gb/s (current: 6.0 Gb/s)
Local Time is:    Fri Jan 19 12:12:25 2018 UTC
SMART support is: Available - device has SMART capability.
SMART support is: Enabled

=== START OF READ SMART DATA SECTION ===
SMART overall-health self-assessment test result: PASSED

General SMART Values:
Offline data collection status:  (0x00)	Offline data collection activity
					was never started.
					Auto Offline Data Collection: Disabled.
Self-test execution status:      (   0)	The previous self-test routine completed
					without error or no self-test has ever 
					been run.
Total time to complete Offline 
data collection: 		(   10) seconds.
Offline data collection
capabilities: 			 (0x15) SMART execute Offline immediate.
					No Auto Offline data collection support.
					Abort Offline collection upon new
					command.
					No Offline surface scan supported.
					Self-test supported.
					No Conveyance Self-test supported.
					No Selective Self-test supported.
SMART capabilities:            (0x0003)	Saves SMART data before entering
					power-saving mode.
					Supports SMART auto save timer.
Error logging capability:        (0x01)	Error logging supported.
					General Purpose Logging supported.
Short self-test routine 
recommended polling time: 	 (   1) minutes.
Extended self-test routine
recommended polling time: 	 (  10) minutes.
SCT capabilities: 	       (0x003d)	SCT Status supported.
					SCT Error Recovery Control supported.
					SCT Feature Control supported.
					SCT Data Table supported.

SMART Attributes Data Structure revision number: 1
Vendor Specific SMART Attributes with Thresholds:
ID# ATTRIBUTE_NAME          FLAG     VALUE WORST THRESH TYPE      UPDATED  WHEN_FAILED RAW_VALUE
  5 Reallocated_Sector_Ct   0x0003   100   100   000    Pre-fail  Always       -       0
 12 Power_Cycle_Count       0x0003   100   100   000    Pre-fail  Always       -       1490
175 Program_Fail_Count_Chip 0x0003   100   100   000    Pre-fail  Always       -       0
176 Erase_Fail_Count_Chip   0x0003   100   100   000    Pre-fail  Always       -       0
177 Wear_Leveling_Count     0x0003   100   100   000    Pre-fail  Always       -       29960
178 Used_Rsvd_Blk_Cnt_Chip  0x0003   100   100   000    Pre-fail  Always       -       0
179 Used_Rsvd_Blk_Cnt_Tot   0x0003   100   100   000    Pre-fail  Always       -       0
180 Unused_Rsvd_Blk_Cnt_Tot 0x0033   100   100   000    Pre-fail  Always       -       1568
181 Program_Fail_Cnt_Total  0x0003   100   100   000    Pre-fail  Always       -       0
182 Erase_Fail_Count_Total  0x0003   100   100   000    Pre-fail  Always       -       0
187 Reported_Uncorrect      0x0003   100   100   000    Pre-fail  Always       -       0
195 Hardware_ECC_Recovered  0x0003   100   100   000    Pre-fail  Always       -       0
241 Total_LBAs_Written      0x0003   100   100   000    Pre-fail  Always       -       149579
242 Total_LBAs_Read         0x0003   100   100   000    Pre-fail  Always       -       185442

SMART Error Log Version: 0
No Errors Logged

SMART Self-test log structure revision number 1
Num  Test_Description    Status                  Remaining  LifeTime(hours)  LBA_of_first_error
# 1  Short offline       Completed without error       00%       705         -
# 2  Short offline       Completed without error       00%         0         -

Selective Self-tests/Logging not supported

Wear_Leveling_Count     0x0003   100   100   000    Pre-fail  Always       -       29960