Search notes:

/proc/sys/fs/binfmt_misc/WSLInterop

On Windows Subsystem for Linux: 
$ cat /proc/sys/fs/binfmt_misc/WSLInterop
enabled
interpreter /tools/init
flags: F
offset 0
magic 4d5a
0x4d5a is MZ

Enabling/disabling WSL interoperability

WSL Interoperability can allegedly be enabled or disabled by writing a 1 or 0 to the file. However, when I tried that, I got a bash: /proc/sys/fs/binfmt_misc/WSLInterop: Permission denied error message. 
$ echo 0 > /proc/sys/fs/binfmt_misc/WSLInterop
-bash: /proc/sys/fs/binfmt_misc/WSLInterop: Permission denied
$ sudo echo 1 > /proc/sys/fs/binfmt_misc/WSLInterop
-bash: /proc/sys/fs/binfmt_misc/WSLInterop: Permission denied

See also

According to this Superuser answer, the presence of /proc/sys/fs/binfmt_misc/WSLInterop is a pretty good indicator that the Kernel is running in Windows Subsystem for Linux.

Index

Fatal error: Uncaught PDOException: SQLSTATE[HY000]: General error: 8 attempt to write a readonly database in /home/httpd/vhosts/renenyffenegger.ch/php/web-request-database.php:78 Stack trace: #0 /home/httpd/vhosts/renenyffenegger.ch/php/web-request-database.php(78): PDOStatement->execute(Array) #1 /home/httpd/vhosts/renenyffenegger.ch/php/web-request-database.php(30): insert_webrequest_('/notes/Linux/fh...', 1761380703, '216.73.216.115', 'Mozilla/5.0 App...', NULL) #2 /home/httpd/vhosts/renenyffenegger.ch/httpsdocs/notes/Linux/fhs/proc/sys/fs/binfmt_misc/WSLInterop(54): insert_webrequest() #3 {main} thrown in /home/httpd/vhosts/renenyffenegger.ch/php/web-request-database.php on line 78