Fixing the qemu serial console terminal size.

Qemu can allow you to attach to a serial console of your guest. This is done with either -nographic or -serial mon:stdio. Its great for getting text output, but after you’ve logged in, you may find issues editing long command lines or using an editor such as vi.

To fix this, you simply need to tell linux what the terminal size you’re using is.

First, figure out what your terminal size is. You have to do this before connecting to qemu, or some other way such as another tmux window or terminal.

• With bash via $LINES and $COLUMNS:

   $ echo rows $LINES columns $COLUMNS
   rows 75 columns 120
  

• With stty, look for ‘rows’ and ‘columns’ below:

   $ stty -a
   speed 38400 baud; rows 75; columns 120; line = 0;
   intr = ^C; quit = ^\; erase = ^?; kill = ^U; eof = ^D; eol = <undef>;
   eol2 = <undef>; swtch = <undef>; start = ^Q; stop = ^S; susp = ^Z; rprnt = ^R;
   werase = ^W; lnext = ^V; discard = ^O; min = 1; time = 0;
   -parenb -parodd -cmspar 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 -flusho -extproc
  
   $ echo $TERM
   xterm
  

Then tell linux inside qemu about it via stty:

$ stty rows 75 columns 120

# now show what it is
$ stty -a |head -n 1
speed 115200 baud; rows 75; columns 120; line = 0;

Last, you probably want to update your TERM variable :

$ export TERM=xterm

Thats it.