HACKER Q&A
📣 Curiositry

I miss CTRL+ALT+DELETE, what's the Linux equivalent?


I've been using Linux for most of my life, and the Windows feature I miss most is CTRL+ALT+DELETE for recovering from freezes.

When your Linux system freezes, what do you do to recover functionality?

(At the point a Linux system has frozen, it's usually too late to summon a command prompt with Ctrl+Alt+F3. The Magic SysRq Key seems like it should be able to duplicate the functionality of CTRL+ALT+DELETE — but so far I haven't successfully used it to recover from freezes, and it isn't usually enabled on friend's computers.)

  👤 LinuxBender Accepted Answer ✓
What you are probably looking for is the magic SysRq key [1] If you enable sysrq then you can send key-sequences directly to the kernel to do things like emergency file system sync, emergency dismount of filesystems, reboot, panic and so on. Not all keyboards have a SysRq key so you may have to map something as that key.

    grep sysr /etc/sysctl.conf
    kernel.sysrq = 1
One can also re-map cntrl+alt+del to do anything if the system is not entirely hung and that configuration incantation varies by what init system your machine is using.

Another thing to research is tuning options like vm.min_free_kbytes, vm.swappiness, vm.lowmem_reserve_ratio, vm.user_reserve_kbytes, vm.admin_reserve_kbytes, vm.overcommit_ratio and vm.overcommit_memory in /etc/sysctl.conf to swap early, and reserve more memory for the kernel based on how much installed RAM you have available. Just setting vm.overcommit_ratio to 0 can solve some hung systems for a number of people at the expense of some applications not launching when memory is low. Another thing to research if you do not have enough RAM is zswap, especially useful to reduce writes to SSD's. To see if your kernel has zswap support:

    modprobe configs && zcat /proc/config.gz | grep -i zswap|grep -v ^#
[1] - https://www.kernel.org/doc/html/v4.15/admin-guide/sysrq.html
👤 drpixie
If your system has frozen and you can't get a terminal with ctrl+alt+F1 (or F2 etc) then consider it dead, and hit the hardware reset or power.

You do have a hardware reset button?

👤 verdverm
top or htop in the terminal