How can I monitor the TBW on my Samsung SSD?

This feature probably wasn't around back then in gnome-disks???

my drive doesn't report this, apparently (at least not in this tool?)

How to find the information

We can use smartctl to find the value of TBW.

1. Install smartctl with $ sudo apt install smartmontools

2. Get sector size and LBA written with $ sudo smartctl -Ai /dev/sda in this case for device /dev/sda

3. Some math: [sector size] * [LBA written] / 1024^3 = X GiB written so far

Example for device /dev/sda

$ sudo smartctl -Ai /dev/sda | grep -E 'Sector Size|Total_LBAs_Written'
Sector Size:      512 bytes logical/physical
241 Total_LBAs_Written      0x0032   099   099   000    Old_age   Always       -       1214641768

$ calc 1214641768*512/1024^3
    579.186328887939453125

In this case the sector size is 512 bytes, which is common, and total LBA written is 1214641768. The result is 579 GiB written so far. This makes sense since this drive is relatively new.

_{Command calc can be install with $ sudo apt install calc or use something else.}

More info

The command $ sudo smartctl -A /dev/sda gives information on "vendor specific SMART Attributes" meaning what your drive shows may not be the same as this one. In the example I used a Samsung SSD which has the needed information.

The accepted answer has bloated output, too much useless script-wizardry and hides initial parameter names from smartctl. Here is a better version;

#!/bin/bash

device=${1:-/dev/sda}
sudo smartctl -A $device |awk '
$0 ~ /Power_On_Hours/ { poh=$10; printf "%s / %d hours / %d days / %.2f yearsn",  $2, $10, $10 / 24, $10 / 24 / 365.25 }
$0 ~ /Total_LBAs_Written/ {
    lbas=$10;
    bytes=$10 * 512;
    mb= bytes / 1024^2;
    gb= bytes / 1024^3;
    tb= bytes / 1024^4;
    printf "%s / %s  / %d mb / %.1f gb / %.3f tbn", $2, $10, mb, gb, tb
    printf "mean writes per hour:  / %.2f",  mb/poh
}
$0 ~ /Airflow_Temperature_Cel/ { print $2 " / " $10}
$0 ~ /Wear_Leveling_Count/ { printf "%s / %d (%% health)n", $2, int($4) }
' |
    sed -e 's:/:@:' |
    sed -e "s$^$$device @ $" |
    column -ts@

sample output:

$ for i in /dev/sd{a,b,c,d}; do ssd-tbw $i;done   |sort -k2,2
/dev/sda    Airflow_Temperature_Cel    49
/dev/sdb    Airflow_Temperature_Cel    49
/dev/sdc    Airflow_Temperature_Cel    45
/dev/sdd    Airflow_Temperature_Cel    47
/dev/sda    mean writes per hour:      655.80
/dev/sdb    mean writes per hour:      646.97
/dev/sdc    mean writes per hour:      874.49
/dev/sdd    mean writes per hour:      733.95
/dev/sda    Power_On_Hours             27292 hours / 1137 days / 3.11 years
/dev/sdb    Power_On_Hours             27300 hours / 1137 days / 3.11 years
/dev/sdc    Power_On_Hours             14432 hours / 601 days / 1.65 years
/dev/sdd    Power_On_Hours             23255 hours / 968 days / 2.65 years
/dev/sda    Total_LBAs_Written         36655329806  / 17898110 mb / 17478.6 gb / 17.069 tb
/dev/sdb    Total_LBAs_Written         36172538301  / 17662372 mb / 17248.4 gb / 16.844 tb
/dev/sdc    Total_LBAs_Written         25846999325  / 12620605 mb / 12324.8 gb / 12.036 tb
/dev/sdd    Total_LBAs_Written         34955224738  / 17067980 mb / 16668.0 gb / 16.277 tb
/dev/sda    Wear_Leveling_Count        93 (% health)
/dev/sdb    Wear_Leveling_Count        93 (% health)
/dev/sdc    Wear_Leveling_Count        95 (% health)
/dev/sdd    Wear_Leveling_Count        94 (% health)

and the one-liner

$ sudo /usr/sbin/smartctl -A /dev/sda | 
     awk '$0~/LBAs/{ printf "TBW %.1fn", $10 * 512 / 1024^4 }'
TBW 17.1

Crucial SSD Lifetime remaining

For Crucial SSD (made by Micron) the question of remaining lifetime is made a little easier.

https://www.micron.com/~/media/documents/products/technical-note/solid-state-storage/tnfd22_client_ssd_smart_attributes.pdf

This doc identifies 202 as Percent Lifetime Remaining. As an example on Ubuntu 16.04 (sudo smartctl /dev/sda1 -a) reports 202 as unknown, but the value of 90 (in my case) matches the description in the pdf, and indicates 90% life remaining. This can be appropriately scaled by the TBW that is given in the crucial.com literature on the drive that you have. Actually, lifetime remaining is rather more useful.