Some things won't respond to Ctrl+C; in that case, you can also do Ctrl+Z which stops the process and then kill %1 - or even fg to go back to it. Read the section in man bash entitled "JOB CONTROL" for more information. It's very helpful. (If you're not familiar with man or the man pager, you can search using /. man bash then inside it /JOB CONTROLEnter will start searching, n will find the next match which is the right section.)

Ctrl+C works for me. When I use the F command in less, it says "(interrupt to abort)". The "interrupt" that it's referring to is whatever key is bound to the terminal interrupt. The command stty -a shows the relevant terminal settings:

speed 38400 baud; rows 50; columns 80; line = 0; intr = ^C; quit = ^; erase = ^H; kill = ^U; eof = ^D; eol = ; eol2 = ; swtch = ; start = ^Q; stop = ^S; susp = ^Z; rprnt = ^R; werase = ^W; lnext = ^V; flush = ^O; min = 1; time = 0; -parenb -parodd cs8 -hupcl -cstopb cread -clocal -crtscts -ignbrk -brkint -ignpar -parmrk -inpck -istrip -inlcr -igncr icrnl ixon -ixoff -iuclc -ixany -imaxbel -iutf8 opost -olcuc -ocrnl onlcr -onocr -onlret -ofill -ofdel nl0 cr0 tab0 bs0 vt0 ff0 isig icanon iexten echo echoe echok -echonl -noflsh -xcase -tostop -echoprt echoctl echoke

It's the intr = ^C that shows that interrupt is generated by Ctrl+C.

If you do stty -a what does it show?

The command stty -a will show you all keyboard shortcuts in your current terminal. Generally in Unix-like systems, the only signals mapped are Ctrl+C (SIGINT), Ctrl+\ (SIGQUIT), and Ctrl+Z (SIGTSTP). There are no other bindings to other signals, and therefore no other signals that you can send within your current session with the keyboard.

Generally speaking, the final d in a program's name usually indicates "daemon". Daemons are intended to run in background and operate through other means beyond stdin/out (like pipes, signals, sockets...). That means that it could be that you get unexpected behavior when the program itself is not running in background (like the terminal seems to "hang", because the daemon has done something to the input, output, or it's doing something/waiting in a loop)

Also generally, it could be as well that the daemon has traps for specific signals and handles them differently (or even ignores them). Have you tried to send SIGINT (kill -2, equivalent to Ctrl+C), SIGQUIT (kill -3, equivalent to Ctrl+\), or SIGTSTP (kill -20, equivalent to Ctrl+Z) while running mysqld in background, just for testing purposes?

EDIT: To change stty mappings, you'll need to write:

stty <action> <new-mapping>

For example, to remap SIGINT to Ctrl+X

stty intr ^x

Note that this setting is only valid in the current terminal during the current session.

As of GNU bash, version 4.4.19(1)-release (x86_64-pc-linux-gnu) and I am not using a VM:

echo $(yes) 

exists the shell and does not freeze the system, and:

ls /*/../*/../*/../*/../*/

returns

bash: /bin/ls: Argument list too long

But as a rule, when you dealing with something that could get all the resources of a system is better to set limits before running, if you know that a process could be a cpu hog you could start it with cpulimit or run renice.

If you want to limit the processes that are already started, you will have to do it one by one by PID, but you can have a batch script to do that like the one below:

#!/bin/bash
LIMIT_PIDS=$(pgrep tesseract)   # PIDs in queue replace tesseract with your name
echo $LIMIT_PIDS
for i in $LIMIT_PIDS
do
    cpulimit -p $i -l 10 -z &   # to 10 percent processes
done

In my case pypdfocr launches the greedy tesseract.

Also in some cases were your CPU is pretty good you can just use a renice like this:

watch -n5 'pidof tesseract | xargs -L1 sudo renice +19'

Look at the screen command which lets you keep running a shell session on a server even when you're disconnected. You can later connect to the same session and see its progress.

As far as I know, the only signals that have a default keyboard shortcut in the shell are SIGINT (Ctrl + C) to stop a process and SIGTSTP (Ctrl + Z) to pause one.

Apparently, as Radu Rădeanu just taught me, there is also Ctrl+\ which is mapped to SIGQUIT.

You can find a list of all signals and what they do in man 7 signal:

   Signal     Value     Action   Comment
   ──────────────────────────────────────────────────────────────────────
   SIGHUP        1       Term    Hangup detected on controlling terminal
                                 or death of controlling process
   SIGINT        2       Term    Interrupt from keyboard
   SIGQUIT       3       Core    Quit from keyboard
   SIGILL        4       Core    Illegal Instruction
   SIGABRT       6       Core    Abort signal from abort(3)
   SIGFPE        8       Core    Floating point exception
   SIGKILL       9       Term    Kill signal
   SIGSEGV      11       Core    Invalid memory reference
   SIGPIPE      13       Term    Broken pipe: write to pipe with no
                                 readers
   SIGALRM      14       Term    Timer signal from alarm(2)

   SIGTERM      15       Term    Termination signal
   SIGUSR1   30,10,16    Term    User-defined signal 1
   SIGUSR2   31,12,17    Term    User-defined signal 2
   SIGCHLD   20,17,18    Ign     Child stopped or terminated
   SIGCONT   19,18,25    Cont    Continue if stopped
   SIGSTOP   17,19,23    Stop    Stop process
   SIGTSTP   18,20,24    Stop    Stop typed at terminal
   SIGTTIN   21,21,26    Stop    Terminal input for background process
   SIGTTOU   22,22,27    Stop    Terminal output for background process
   SIGBUS      10,7,10     Core    Bus error (bad memory access)
   SIGPOLL                 Term    Pollable event (Sys V).
                                   Synonym for SIGIO
   SIGPROF     27,27,29    Term    Profiling timer expired
   SIGSYS      12,31,12    Core    Bad argument to routine (SVr4)
   SIGTRAP        5        Core    Trace/breakpoint trap
   SIGURG      16,23,21    Ign     Urgent condition on socket (4.2BSD)
   SIGVTALRM   26,26,28    Term    Virtual alarm clock (4.2BSD)
   SIGXCPU     24,24,30    Core    CPU time limit exceeded (4.2BSD)
   SIGXFSZ     25,25,31    Core    File size limit exceeded (4.2BSD)

   SIGIOT         6        Core    IOT trap. A synonym for SIGABRT
   SIGEMT       7,-,7      Term
   SIGSTKFLT    -,16,-     Term    Stack fault on coprocessor (unused)
   SIGIO       23,29,22    Term    I/O now possible (4.2BSD)
   SIGCLD       -,-,18     Ign     A synonym for SIGCHLD
   SIGPWR      29,30,19    Term    Power failure (System V)
   SIGINFO      29,-,-             A synonym for SIGPWR
   SIGLOST      -,-,-      Term    File lock lost (unused)
   SIGWINCH    28,28,20    Ign     Window resize signal (4.3BSD, Sun)
   SIGUNUSED    -,31,-     Core    Synonymous with SIGSYS

You can see the signals that are available on your system with kill -l:

$ kill -l
 1) SIGHUP      2) SIGINT        3) SIGQUIT      4) SIGILL      5) SIGTRAP
 6) SIGABRT     7) SIGBUS        8) SIGFPE       9) SIGKILL     10) SIGUSR1
11) SIGSEGV     12) SIGUSR2     13) SIGPIPE     14) SIGALRM     15) SIGTERM
16) SIGSTKFLT   17) SIGCHLD     18) SIGCONT     19) SIGSTOP     20) SIGTSTP
21) SIGTTIN     22) SIGTTOU     23) SIGURG      24) SIGXCPU     25) SIGXFSZ
26) SIGVTALRM   27) SIGPROF     28) SIGWINCH    29) SIGIO       30) SIGPWR
31) SIGSYS      34) SIGRTMIN    35) SIGRTMIN+1  36) SIGRTMIN+2  37) SIGRTMIN+3
38) SIGRTMIN+4  39) SIGRTMIN+5  40) SIGRTMIN+6  41) SIGRTMIN+7  42) SIGRTMIN+8
43) SIGRTMIN+9  44) SIGRTMIN+10 45) SIGRTMIN+11 46) SIGRTMIN+12 47) SIGRTMIN+13
48) SIGRTMIN+14 49) SIGRTMIN+15 50) SIGRTMAX-14 51) SIGRTMAX-13 52) SIGRTMAX-12
53) SIGRTMAX-11 54) SIGRTMAX-10 55) SIGRTMAX-9  56) SIGRTMAX-8  57) SIGRTMAX-7
58) SIGRTMAX-6  59) SIGRTMAX-5  60) SIGRTMAX-4  61) SIGRTMAX-3  62) SIGRTMAX-2
63) SIGRTMAX-1  64) SIGRTMAX    

Note that there are many SIGRTMAX and SIGRTMIN signals, the Linux kernel supports 32 different signals but the range of signals actually supported will depend on the glibc implementation on your system.