11. Processes

Files and filesystems

Filesystem objects:

• files
• directories
• symlinks
• devices
• pipes (aka FIFOs)

  • mkfifo and example

  • pipe

    • note two descriptors

    • this is unnamed pipe (use mkfifo for named one)

• sockets (aka i've got a hole in me pocket)

  • async!
• …

Filesystem Hierarchy Standard

• non-strictness (but…)
• useful directories of Linux-based system

Mounting

• virtual filesystems (/proc, /sys, /dev, thousands of them)

• lsblk, fdisk -l устройство

• mount (⇒ mount)

  • e. g. mount /dev/sda1 /mnt/disk/

Putting in all together

statstat(const char *pathname, struct stat *statbuf);

• struct stat

• note special types *_t (mostly unsigned integers, filesystem type depended)

• stat utility

Process

• Processes.

  • PID. Process creation, process tree ps -ef --forest

  • Parent_process: child, zombie, orphan, PID 1

exec (IRL many others)

• keeps PID

• replaces memory

• inherits open files and environment

fork (IRL clone)

• new PID

• copy memory (probably COW, e. g. no copy for .text)

• copy environment variables

  • ⇒ cannot change parent environment

  • can be re-created (see main(argc, char *argv[], char *envp[]))

• inherit open files (descriptors)

• fork() returns

  • child PID to parent
  • 0 to child

wait

• wait(NULL)

• macros to decode wstatus

I/O redirection for child

• cmd > file

  • fork()

  • child closes stdout (descriptor 1) and opens file (at this descriptor)

  • exec(cmd)

  • parent waits for child

• cmd < file

  • guess what

• dup

• cmd1 | cmd2

  0. parent creates a pipe pair
  1. parent forks to child (1.)
     • closes stdout (descriptor 1)
     • dups writeable part of pipe (1 element)
       • ⇒ stdout becames pipe[1]
       • closes readable part of pipe (for current PID only)

       • execs cmd1 (now writing to pipe[1])

  2. parent forks
     • closes stdin (descriptor 0)
     • dups readable part of pipe (0 element)
       • ⇒ stdin becames pipe[0]
       • closes writeable part of pipe (for current PID only)

       • execs cmd2 (now reading from pipe[0])

  3. parent waits for both childs

H/W

TODO