It used to be that you had to upgrade in multiple steps, but not anymore. You can upgrade directly from 1.12.0 to 1.13.2
Make sure you backup your database
After neglecting upgrades so long I upgraded to newest versions, to fix broken bootstrap links. All went better than last update from 1.1.2 to 1.5.x. First I did backups, and test upgrade, and then live version, all ok. Now about 12 hours later forum crashed.
I also upgraded Node to newest LTS version (8.11.1), previous version was running with 6.x.
At log I have 4 of these:
2018-04-07T11:10:49.148Z  - info: [app] Shutdown (SIGTERM/SIGINT) Initialised. 2018-04-07T11:10:49.147Z  - error: TypeError: Cannot read property 'hasOwnProperty' of null at postParse (/nodebb/node_modules/nodebb-plugin-markdown/index.js:181:15) at /nodebb/node_modules/async/dist/async.js:66:19 at nextTask (/nodebb/node_modules/async/dist/async.js:5310:14) at next (/nodebb/node_modules/async/dist/async.js:5317:9) at /nodebb/node_modules/async/dist/async.js:958:16 at _combinedTickCallback (internal/process/next_tick.js:138:11) at process._tickCallback (internal/process/next_tick.js:180:9) 2018-04-07T11:10:49.160Z  - info: [app] Web server closed to connections. 2018-04-07T11:10:49.169Z  - info: [app] Database connection closed. 2018-04-07T11:10:49.170Z  - info: [app] Shutdown complete. [cluster] Child Process (39) has exited (code: 1, signal: null) [cluster] Spinning up another process...
3 restarts in 10 seconds, most likely an error on startup. Halting.
What others Plugins are you using? You can use
./nodebb plugins to print out a list. Try disabling them, as it seems one is passing an invalid value to markdown.
Only default? plugins, haven't installed or deactivated any, default set was also used with 1.5.0
At least emojis in link do not crash markdown (i tested this at own local installation first ).
Should this be reported to GitHub as separated issue?
# Example for markdown :smile: [test](http://www:heart:com)
After last restart forum has been up almost 2 days without crash, no plugin has been disabled. Actually I didn't do anything else, just started NodeBB again.