*It appears like the file is indeed locked when opening it, but this lock *is ignored by /cat/! It is not ignored when opened by another COBOL *program, though. * *If viewing on glot.io, do checkout the run settings tab, which has a *custom command for running multiple concurrent instances of this *program. IDENTIFICATION DIVISION. PROGRAM-ID. example. ENVIRONMENT DIVISION. INPUT-OUTPUT SECTION. FILE-CONTROL. SELECT OPTIONAL fd-example ASSIGN TO 'example.txt' ACCESS IS SEQUENTIAL ORGANIZATION IS RECORD SEQUENTIAL. DATA DIVISION. FILE SECTION. FD fd-example. 01 fs-example PIC X(11). PROCEDURE DIVISION. MOVE 'HELLO WORLD' TO fs-example OPEN EXTEND fd-example WRITE fs-example CALL 'C$SLEEP' USING 2 CLOSE fd-example EXIT PROGRAM .