Is steady clock steady system wide?

I am using FastRTPS to communicate between multiple processes on a single Linux system. They are exchanging information in packets. Every packet has a time stamp independent of its sending or receiving time. This way the conveyed information can be used correctly.

I was thinking on using:

uint64_t time_in_microseconds = std::chrono::duration_cast
          <std::chrono::microseconds>(std::chrono::steady_clock::now()
          .time_since_epoch()).count(); 

to get the timestamp for the packets.

However, is steady clock steady across processes on a single system? Or only inside a single process?

If not, how much does the system clock vary under normal conditions? How much would it move "back in time"? (not adjusting it manually, no internet connection, no time change, etc.)

Thank you