I love UNIX and so can you

I love UNIX and so can you

58376779023f009fc13d160bb3e82515?s=128

John Downey

July 14, 2016
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  1. 9.

    1. a hierarchical file system incorporating demountable volumes 2. compatible

    file, device, and inter-process I/O 3. the ability to initiate asynchronous processes 4. system command language selectable on a per-user basis 5. over 100 subsystems including a dozen languages @jtdowney 9
  2. 10.

    Why was UNIX successful 1. The UNIX system was written

    in a high-level language. 2. The UNIX system was distributed in source form. 3. The UNIX system provided powerful primitives normally found in only those operating systems that ran on much more expensive hardware. @jtdowney 10
  3. 15.

    Officially it means 4 POSIX 4 Single UNIX Specification 4

    The Open Group certifies compatible systems 4 Solaris 4 OS X @jtdowney 15
  4. 17.

    Unofficially 4 UNIX-like systems 4 POSIX 4 Aren't certified for

    the Single UNIX Specification 4 Linux 4 BSD (Free/Net/Open) 4 illumos @jtdowney 17
  5. 19.

    UNIX Philosophy 4 Write programs that do one thing and

    do it well. 4 Write programs to work together. 4 Write programs to handle text streams, because that is a universal interface. @jtdowney 19
  6. 20.

    Functional operations on data 4 filter (grep) 4 map (sed

    / awk) 4 reduce (uniq / wc / awk) @jtdowney 20
  7. 23.

    netstat -an % lsof -p 9576 COMMAND PID USER FD

    TYPE DEVICE SIZE/OFF NODE NAME netstat 9576 pair cwd DIR 202,1 4096 8787609 /home/pair/bt/vault netstat 9576 pair rtd DIR 202,1 4096 2 / netstat 9576 pair txt REG 202,1 119784 10616898 /bin/netstat netstat 9576 pair mem REG 202,1 1607696 2886783 /lib/x86_64-linux-gnu/libc-2.13.so netstat 9576 pair mem REG 202,1 136936 2886666 /lib/x86_64-linux-gnu/ld-2.13.so netstat 9576 pair mem REG 202,1 1534672 11798922 /usr/lib/locale/locale-archive netstat 9576 pair 0u CHR 136,3 0t0 6 /dev/pts/3 netstat 9576 pair 1u CHR 136,3 0t0 6 /dev/pts/3 netstat 9576 pair 2u CHR 136,3 0t0 6 /dev/pts/3 @jtdowney 23
  8. 24.

    COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME netstat

    9576 pair 0u CHR 136,3 0t0 6 /dev/pts/3 netstat 9576 pair 1u CHR 136,3 0t0 6 /dev/pts/3 netstat 9576 pair 2u CHR 136,3 0t0 6 /dev/pts/3 @jtdowney 24
  9. 26.

    Every process starts with 3 file descriptors open 4 0

    = STDIN 4 1 = STDOUT 4 2 = STDERR @jtdowney 26
  10. 27.

    COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME netstat

    9576 pair 0u CHR 136,3 0t0 6 /dev/pts/3 netstat 9576 pair 1u CHR 136,3 0t0 6 /dev/pts/3 netstat 9576 pair 2u CHR 136,3 0t0 6 /dev/pts/3 @jtdowney 27
  11. 28.

    netstat -an | grep -i established % lsof -p 12538

    COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME netstat 12538 pair cwd DIR 202,1 4096 8787609 /home/pair/bt/vault netstat 12538 pair rtd DIR 202,1 4096 2 / netstat 12538 pair txt REG 202,1 119784 10616898 /bin/netstat netstat 12538 pair mem REG 202,1 1607696 2886783 /lib/x86_64-linux-gnu/libc-2.13.so netstat 12538 pair mem REG 202,1 136936 2886666 /lib/x86_64-linux-gnu/ld-2.13.so netstat 12538 pair mem REG 202,1 1534672 11798922 /usr/lib/locale/locale-archive netstat 12538 pair 0u CHR 136,3 0t0 6 /dev/pts/3 netstat 12538 pair 1w FIFO 0,8 0t0 735322872 pipe netstat 12538 pair 2u CHR 136,3 0t0 6 /dev/pts/3 @jtdowney 28
  12. 29.

    netstat -an | grep -i established % lsof -p 12539

    COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME grep 12539 pair cwd DIR 202,1 4096 8787609 /home/pair/bt/vault grep 12539 pair rtd DIR 202,1 4096 2 / grep 12539 pair txt REG 202,1 175488 10616876 /bin/grep grep 12539 pair mem REG 202,1 1607696 2886783 /lib/x86_64-linux-gnu/libc-2.13.so grep 12539 pair mem REG 202,1 14768 2886786 /lib/x86_64-linux-gnu/libdl-2.13.so grep 12539 pair mem REG 202,1 136936 2886666 /lib/x86_64-linux-gnu/ld-2.13.so grep 12539 pair mem REG 202,1 1534672 11798922 /usr/lib/locale/locale-archive grep 12539 pair mem REG 202,1 26066 11807983 /usr/lib/x86_64-linux-gnu/gconv/gconv-modules.cache grep 12539 pair 0r FIFO 0,8 0t0 735322872 pipe grep 12539 pair 1u CHR 136,3 0t0 6 /dev/pts/3 grep 12539 pair 2u CHR 136,3 0t0 6 /dev/pts/3 @jtdowney 29
  13. 31.

    grep test < /dev/zero % lsof -p 13828 COMMAND PID

    USER FD TYPE DEVICE SIZE/OFF NODE NAME grep 13828 pair cwd DIR 202,1 4096 7864322 /home/pair grep 13828 pair rtd DIR 202,1 4096 2 / grep 13828 pair txt REG 202,1 175488 10616876 /bin/grep grep 13828 pair mem REG 202,1 1607696 2886783 /lib/x86_64-linux-gnu/libc-2.13.so grep 13828 pair mem REG 202,1 14768 2886786 /lib/x86_64-linux-gnu/libdl-2.13.so grep 13828 pair mem REG 202,1 136936 2886666 /lib/x86_64-linux-gnu/ld-2.13.so grep 13828 pair mem REG 202,1 1534672 11798922 /usr/lib/locale/locale-archive grep 13828 pair mem REG 202,1 26066 11807983 /usr/lib/x86_64-linux-gnu/gconv/gconv-modules.cache grep 13828 pair 0r CHR 1,5 0t0 1030 /dev/zero grep 13828 pair 1u CHR 136,3 0t0 6 /dev/pts/3 grep 13828 pair 2u CHR 136,3 0t0 6 /dev/pts/3 @jtdowney 31
  14. 34.

    % strace cat test execve("/bin/cat", ["cat", "test"], [/* 86 vars

    */]) = 0 ... open("test", O_RDONLY) = 3 read(3, "Hello World\n", 32768) = 12 write(1, "Hello World\n", 12) = 12 read(3, "", 32768) = 0 close(3) = 0 close(1) = 0 close(2) = 0 exit_group(0) = ? @jtdowney 34
  15. 35.

    Common file-related system calls 4 creat - create a file

    4 open - open a file 4 read - read from a file descriptor 4 write - write to a file descriptor 4 close - close a file descriptor @jtdowney 35
  16. 36.

    Expose special files in mount points % mount sysfs on

    /sys type sysfs (rw,nosuid,nodev,noexec,relatime) proc on /proc type proc (rw,nosuid,nodev,noexec,relatime) udev on /dev type devtmpfs (rw,relatime,size=10240k,nr_inodes=3855906,mode=755) devpts on /dev/pts type devpts (rw,nosuid,noexec,relatime,gid=5,mode=620,ptmxmode=000) tmpfs on /run type tmpfs (rw,nosuid,noexec,relatime,size=3089000k,mode=755) /dev/xvda1 on / type ext4 (rw,relatime,stripe=128,data=ordered) tmpfs on /run/lock type tmpfs (rw,nosuid,nodev,noexec,relatime,size=5120k) tmpfs on /run/shm type tmpfs (rw,nosuid,nodev,noexec,relatime,size=6177980k) @jtdowney 36
  17. 37.

    % ls /proc 1/ 111/ 13717/ 17293/ 20/ 26/ 28952/

    34/ 4125/ 44/ 4716/ 10/ 112/ 13719/ 173/ 208/ 26538/ 28962/ 35/ 4136/ 4403/ 4718/ 100/ 113/ 13720/ 174/ 209/ 26549/ 29/ 36/ 42/ 4422/ 4721/ 101/ 117/ 13926/ 176/ 21/ 267/ 3/ 37/ 4236/ 4445/ 4723/ 102/ 12/ 14/ 18/ 22/ 27/ 30/ 38/ 4276/ 45/ 4769/ 103/ 13/ 15/ 185/ 23/ 274/ 31/ 39/ 43/ 46/ 4776/ 108/ 13329/ 1533/ 186/ 24/ 28/ 32/ 3980/ 4349/ 4618/ 4778/ 109/ 13334/ 16/ 19/ 249/ 28162/ 33/ 4/ 4361/ 4683/ 4795/ 11/ 13337/ 16276/ 1969/ 25/ 28883/ 335/ 40/ 4366/ 47/ 48/ 110/ 13346/ 17/ 2/ 250/ 28888/ 339/ 41/ 4387/ 4711/ 4806/ @jtdowney 37
  18. 38.

    % ls /proc/self attr/ coredump_filter gid_map mountinfo oom_score sessionid task/

    autogroup cpuset io mounts oom_score_adj smaps timers auxv cwd@ limits mountstats pagemap stack uid_map cgroup environ loginuid net/ personality stat wchan clear_refs exe@ map_files/ ns/ projid_map statm cmdline fd/ maps numa_maps root@ status comm fdinfo/ mem oom_adj sched syscall @jtdowney 38
  19. 39.

    % cat /proc/self/status Name: zsh State: S (sleeping) Tgid: 20292

    Ngid: 0 Pid: 20292 PPid: 7596 TracerPid: 0 Uid: 1000 1000 1000 1000 Gid: 1000 1000 1000 1000 FDSize: 64 Groups: 4 106 918 1000 1100 2000 VmPeak: 45772 kB @jtdowney 39
  20. 41.

    4 pid - process id 4 ppid - parent process

    id 4 uid - user id 4 gid - group id @jtdowney 41
  21. 44.

    What does it get? 4 Get a copy of the

    file descriptors 4 Easy to use pipes for inter-process communication 4 Share virtual memory (copy on write) @jtdowney 44
  22. 45.

    require "logger" logger = Logger.new($stdout) logger.info "starting parent" reader, writer

    = IO.pipe fork do writer.close logger.info "starting child" logger.info reader.gets end reader.close writer.write "sent from parent process" @jtdowney 45
  23. 46.

    % ruby fork_test.rb I, [2016-07-14T16:52:38.440600 #28966] INFO -- : starting

    parent I, [2016-07-14T16:52:38.442533 #28968] INFO -- : starting child I, [2016-07-14T16:52:38.444770 #28968] INFO -- : sent from parent process @jtdowney 46
  24. 48.

    Signal Value Action Comment ────────────────────────────────────────────────────────────────────── SIGHUP 1 Term Hangup detected

    on controlling terminal or death of controlling process SIGINT 2 Term Interrupt from keyboard SIGQUIT 3 Core Quit from keyboard SIGILL 4 Core Illegal Instruction SIGABRT 6 Core Abort signal from abort(3) SIGFPE 8 Core Floating point exception SIGKILL 9 Term Kill signal SIGSEGV 11 Core Invalid memory reference SIGPIPE 13 Term Broken pipe: write to pipe with no readers SIGALRM 14 Term Timer signal from alarm(2) SIGTERM 15 Term Termination signal SIGUSR1 30,10,16 Term User-defined signal 1 SIGUSR2 31,12,17 Term User-defined signal 2 SIGCHLD 20,17,18 Ign Child stopped or terminated SIGCONT 19,18,25 Cont Continue if stopped SIGSTOP 17,19,23 Stop Stop process SIGTSTP 18,20,24 Stop Stop typed at tty SIGTTIN 21,21,26 Stop tty input for background process SIGTTOU 22,22,27 Stop tty output for background process The signals SIGKILL and SIGSTOP cannot be caught, blocked, or ignored. @jtdowney 48
  25. 49.

    4 SIGHUP - sent when you close a terminal on

    a running process 4 SIGINT - sent when you CTRL-C 4 SIGTERM - sent with plain kill <pid> 4 SIGKILL - not messing around, uncatchable @jtdowney 49
  26. 51.

    References 4 Books 4 The Daemon, the Gnu, and the

    Penguin by Peter H. Salus, et al 4 The Design and Implementation of the 4.4 BSD Operating System by Marshall Kirk McKusick, et al 4 Lions' Commentary on Unix 6th Edition by John Lions 4 Papers 4 The UNIX Time-Sharing System by Dennis M. Ritchie and Ken Thompson 4 The Evolution of the Unix Time-sharing System by Dennis M. Ritchie 4 Articles 4 https://en.wikipedia.org/wiki/History_of_Unix 4 https://en.wikipedia.org/wiki/Unix_philosophy @jtdowney 51