I work under python. I declared a serial printer tmt88 9600,N,8,1. When i run a program python with two threads which print a file1 and a file2 on my printer tmt88, why the printed output are mixed sometimes ? Thread 1 every 1 seconde : 'lp -d tmt88 file1' Thread 2 every 1 seconde : 'lp -d tmt88 file2' The printed outputs are mixed from time to time !!!!!!