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network-programmingprocesspidsocat

Why does launching socat with some arguments result in two processes?

Open 3 terminals, which I'll call A, B, and C, and execute the following:

  1. socat TCP-LISTEN:12345,fork - in A,
  2. pidof socat in B,
  3. socat TCP-CONNECT:localhost:12345 - in C,
  4. pidof socat again in B.

Step 2 will print 1 PID, whereas step 4 will print 3 PIDs, meaning that step 3 spawned 2 processes (whereas step 1 definitely spawned only 1).

Why is that? Is it an (uniteresting?) implementation detail of socat? Or is it necessary for socat to work?

Solution

  • It's no surprise socat listener spawns an extra process as it is literally instructed to do so by option fork.

    Removing fork results in just two PIDs printed by step 4.