I ❤ UNIX and so can you @jtdowney 1

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History @jtdowney 6

Research UNIX @jtdowney 7

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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

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

Berkley Software Distribution (BSD) @jtdowney 11

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UNIX Wars @jtdowney 13

What does UNIX mean now? @jtdowney 14

Officially it means 4 POSIX 4 Single UNIX Specification 4 The Open Group certifies compatible systems 4 Solaris 4 OS X @jtdowney 15

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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

❤ @jtdowney 18

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

Functional operations on data 4 filter (grep) 4 map (sed / awk) 4 reduce (uniq / wc / awk) @jtdowney 20

netstat -an | grep -i established @jtdowney 21

Everything is a file (descriptor) @jtdowney 22

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

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

% tty /dev/pts/3 @jtdowney 25

Every process starts with 3 file descriptors open 4 0 = STDIN 4 1 = STDOUT 4 2 = STDERR @jtdowney 26

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

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

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

Shell Redirection @jtdowney 30

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

System Calls @jtdowney 32

% echo "Hello World" > test % cat test Hello World @jtdowney 33

% 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

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

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

% 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

% 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

% 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

Process Model @jtdowney 40

4 pid - process id 4 ppid - parent process id 4 uid - user id 4 gid - group id @jtdowney 41

% pstree init─┬─zsh───pstree ├─7*[getty] ├─2*[master─┬─pickup] │ └─qmgr] ├─atd ├─cron───cron───sh───vpair───{vpair} ├─docker─┬─docker-containe───9*[{docker-containe}] │ └─24*[{docker}] ├─epmd ├─haproxy ├─java───128*[{java}] @jtdowney 42

fork() @jtdowney 43

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

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

% 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

Signals @jtdowney 47

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

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 4 SIGKILL - not messing around, uncatchable @jtdowney 49

Questions @jtdowney 50

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