There are many solutions, but they also have some shortcomings:

• sleep infinity is a top choice, but it is not supported by some libc/musl versions.
• sleep 100000d is good, but will eventually terminate
• tail -f /dev/null wakes up each time some process drops something to /dev/null, and uses inotify resources
• echo 'void main(){ pause(); }' > pause.c; gcc pause.c -o pause; ./pause requires gcc to be installed
• piping from a halted shell with sh -c 'kill -STOP $$' | program > output will keep going even after the program is terminated

A good alternative that avoids these limitations is waiting on a halted process:

while :; do :; done & kill -STOP $! && wait $!

The single ampersand & will put the while loop in the background. The kill will halt it using it’s process id. wait will wait on it indefinitely.