UNIX process environment

Each process has its own virtual environment, including:

• A virtual memory map

  Memory is managed in fixed-size chunks called "pages".

  The map has a number of conventional regions:

  • "text" refers to executable code, often read-only, usually occupying the lowest memory addresses
  • "data" refers to writable data, usually just above "text"
  • "stack" is the CPU stack, usually near the top of the address space
  • Other executable regions corresponding to shared libraries, data regions corresponding to mmap(2)ed files, shared memory, etc.

• A current directory (changed with chdir(2))
• A table of open files (changed with open(2), close(2), others)

  File numbers 0, 1, 2 conventionally refer to standard input, output, and error

• The user id and group id that the process is running under (can be changed with setuid(2) or setgid(2), usually only by the superuser)

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