Daemons are processes on a system which principal characteristics are: Aren’t directly controlled by the user Run in background Are spawned tipically by init manager
Daemons are processes on a system which principal characteristics are: Aren’t directly controlled by the user Run in background Are spawned tipically by init manager Tipically log data into logfiles
Daemons are processes on a system which principal characteristics are: Aren’t directly controlled by the user Run in background Are spawned tipically by init manager Tipically log data into logfiles Are detached from terminal
a process? Is an instance of a computer program that is being executed How processes are created? fork in UNIX, CreateProcess on the rest What is shared between processes?
a process? Is an instance of a computer program that is being executed How processes are created? fork in UNIX, CreateProcess on the rest What is shared between processes? Libraries?
a process? Is an instance of a computer program that is being executed How processes are created? fork in UNIX, CreateProcess on the rest What is shared between processes? Libraries? Memory?
process consisted of? An image of the executable machine code. Virtual memory which includes the executable code, process-specific data, a call stack, and a heap to hold intermediate computation data generated during run time.
process consisted of? An image of the executable machine code. Virtual memory which includes the executable code, process-specific data, a call stack, and a heap to hold intermediate computation data generated during run time. Operating system descriptors of resources, such as file descriptors.
process consisted of? An image of the executable machine code. Virtual memory which includes the executable code, process-specific data, a call stack, and a heap to hold intermediate computation data generated during run time. Operating system descriptors of resources, such as file descriptors. Security attributes, such as the process owner and the process’ set of permissions.
process consisted of? An image of the executable machine code. Virtual memory which includes the executable code, process-specific data, a call stack, and a heap to hold intermediate computation data generated during run time. Operating system descriptors of resources, such as file descriptors. Security attributes, such as the process owner and the process’ set of permissions. Processor state, such as the content of registers, physical memory addressing, etc. The state is typically stored in CPU registers when the process is executing, and in memory otherwise.
: Replaces the current process image Kernel.system : Executes cmd in a subshell Kernel.‘ ( backticks ) : Executes cmd in a subshell IO.popen : Runs command as a subprocess Open3.popen3 Process.spawn Process.daemon IO.popen4 ( JRuby )
program in a new process puts("I am process #{Process.pid}") pid = fork do puts("I am process #{Process.pid}, my parent is #{Process.ppid}") end puts("I am process #{Process.pid}, I am waiting for process #{pid}") Process.wait(pid)
program in a new process puts("I am process #{Process.pid}") pid = fork do puts("I am process #{Process.pid}, my parent is #{Process.ppid}") end puts("I am process #{Process.pid}, I am waiting for process #{pid}") Process.wait(pid) I am process 11135 I am process 11135, I am waiting for process 11137 I am process 11137, my parent is 11135
puts(’I am not going to die!’) end puts(’Trying to kill myself’) Process.kill(:KILL, Process.pid) puts(’I should be alive’) Trying to k i l l myself K i l l e d
a UNIX daemon Dissociate from the controlling tty Become a session leader Become a process group leader Execute as a background task by forking and exiting (once or twice), required sometimes to become a session leader.
a UNIX daemon Dissociate from the controlling tty Become a session leader Become a process group leader Execute as a background task by forking and exiting (once or twice), required sometimes to become a session leader. Setting the root directory (/) as the current working directory so that the process does not keep any directory in use.
a UNIX daemon Dissociate from the controlling tty Become a session leader Become a process group leader Execute as a background task by forking and exiting (once or twice), required sometimes to become a session leader. Setting the root directory (/) as the current working directory so that the process does not keep any directory in use. Changing the umask to 0 to allow operating system calls to provide their own permission masks and not to depend on the umask of the caller
a UNIX daemon Dissociate from the controlling tty Become a session leader Become a process group leader Execute as a background task by forking and exiting (once or twice), required sometimes to become a session leader. Setting the root directory (/) as the current working directory so that the process does not keep any directory in use. Changing the umask to 0 to allow operating system calls to provide their own permission masks and not to depend on the umask of the caller Closing all inherited files at the time of execution that are left open by the parent process, including file descriptors 0, 1 and 2.
a UNIX daemon Dissociate from the controlling tty Become a session leader Become a process group leader Execute as a background task by forking and exiting (once or twice), required sometimes to become a session leader. Setting the root directory (/) as the current working directory so that the process does not keep any directory in use. Changing the umask to 0 to allow operating system calls to provide their own permission masks and not to depend on the umask of the caller Closing all inherited files at the time of execution that are left open by the parent process, including file descriptors 0, 1 and 2. Using a logfile, the console, or /dev/null as stdin, stdout, and stderr
1.9 Process.daemon Detach the process from controlling terminal and run in the background as system daemon. Unless the argument nochdir is true, it changes the current working directory to /. Unless the argument noclose is true, daemon() will redirect standard input, standard output and standard error to /dev/null. Return zero on success, or raise one of Errno::*.
https://github.com/ruby/ruby/blob/master/process.c s t a t i c VALUE proc daemon ( i n t argc , VALUE argv ) { VALUE nochdir , n o c l o s e ; i n t n ; r b s e c u r e (2) ; r b s c a n a r g s ( argc , argv , ”02” , &nochdir , &n o c l o s e ) ; p r e f o r k () ; b e f o r e f o r k ( ) ; n = daemon (RTEST( n oc h di r ) , RTEST( n o c l o s e ) ) ; a f t e r f o r k () ; i f ( n < 0) r b s y s f a i l ( ”daemon” ) ; return INT2FIX ( n ) ; } #d e f i n e daemon ( nochdir , n o c l o s e ) rb daemon ( nochdir , n o c l o s e ) #e n d i f
https://github.com/ruby/ruby/blob/master/process.c s t a t i c i n t rb daemon ( i n t nochdir , i n t n o c l o s e ) { i n t n , e r r = 0 ; switch ( r b f o r k (0 , 0 , 0 , Qnil ) ) { case −1: r b s y s f a i l ( ”daemon” ) ; case 0: break ; d e f a u l t : e x i t (EXIT SUCCESS) ; } p r o c s e t s i d () ; switch ( r b f o r k (0 , 0 , 0 , Qnil ) ) { case −1: return −1; case 0: break ; d e f a u l t : e x i t (EXIT SUCCESS) ; } i f ( ! noch d ir ) e r r = c h d i r ( ”/” ) ; i f ( ! n o c l o s e && ( n = open ( ”/ dev / n u l l ” , O RDWR, 0) ) != −1) { ( void ) dup2 (n , 0) ; ( void ) dup2 (n , 1) ; ( void ) dup2 (n , 2) ; i f ( n > 2) ( void ) c l o s e ( n ) ; } return e r r ; }
https://github.com/ruby/ruby/blob/master/process.c r b p i d t r b f o r k ( i n t ∗status , i n t (∗ chfunc ) ( void ∗) , void ∗charg , VALUE f d s ) { i f ( chfunc ) { s t r u c t c h f u n c w r a p p e r t warg ; warg . chfunc = chfunc ; warg . arg = charg ; return r b f o r k e r r ( status , chfunc wrapper , &warg , fds , NULL, 0) ; } e l s e { return r b f o r k e r r ( status , NULL, NULL, fds , NULL, 0) ; } }
From https://github.com/ruby/ruby/blob/master/process.c r b p i d t r b f o r k e r r ( i n t ∗status , i n t (∗ chfunc ) ( void ∗ , char ∗ , s i z e t ) , void ∗charg , VALUE fds , char ∗errmsg , s i z e t e r r m s g b u f l e n ) { r b p i d t pid ; i n t err , s t a t e = 0 ; #d e f i n e p r e f o r k () ( d e f i n e \ r b i o f l u s h ( r b s t d o u t ) , \ r b i o f l u s h ( r b s t d e r r ) r b s t d e r r \ ) p r e f o r k () ; // STUFF f o r ( ; b e f o r e f o r k ( ) , ( pid = f o r k () ) < 0; p r e f o r k () ) { a f t e r f o r k () ; // STUFF } i f ( ! pid ) { f o r k e d c h i l d = 1 ; i f ( chfunc ) { i f ( !(∗ chfunc ) ( charg , errmsg , e r r m s g b u f l e n ) ) e x i t (EXIT SUCCESS) ; #i f EXIT SUCCESS == 127 e x i t ( EXIT FAILURE ) ; #e l s e e x i t (127) ; #e n d i f } } a f t e r f o r k () ; return pid ; }
https://github.com/ruby/ruby/blob/master/process.c s t a t i c VALUE p r o c s e t s i d ( void ) { r b p i d t pid ; r b s e c u r e (2) ; pid = s e t s i d ( ) ; i f ( pid < 0) r b s y s f a i l (0) ; return PIDT2NUM( pid ) ; } #d e f i n e s e t s i d () r u b y s e t s i d ()
https://github.com/ruby/ruby/blob/master/process.c s t a t i c r b p i d t r u b y s e t s i d ( void ) { r b p i d t pid ; i n t r e t ; pid = g e t p i d ( ) ; #i f d e f i n e d (SETPGRP VOID) r e t = s e t p g r p () ; /∗ I f ‘ p i d t s e t p g r p ( void ) ’ i s e q u i v a l e n t to s e t s i d () , ∗ ‘ r e t ’ w i l l be the same v a l u e as ‘ pid ’ , and f o l l o w i n g open () w i l l f a i l . ∗ In Linux , ‘ i n t s e t p g r p ( void ) ’ i s e q u i v a l e n t to s e t p g i d (0 , 0) . ∗/ #e l s e r e t = s e t p g r p (0 , pid ) ; #e n d i f i f ( r e t == −1) return −1; i f (( fd = open ( ”/ dev / t t y ” , O RDWR) ) >= 0) { i o c t l ( fd , TIOCNOTTY, NULL) ; c l o s e ( fd ) ; } return pid ; } #e n d i f
https://github.com/ruby/ruby/blob/master/process.c s t a t i c VALUE p r o c s e t p g r p ( void ) { r b s e c u r e (2) ; /∗ check f o r p o s i x s e t p g i d () f i r s t ; t h i s matches the p o s i x ∗/ /∗ getpgrp ( ) above . I t appears that c o n f i g u r e w i l l s e t SETPGRP VOID ∗/ /∗ even though s e t p g r p (0 ,0) would be p r e f e r r e d . The p o s i x c a l l a v o i d s ∗/ /∗ t h i s c o n f u s i o n . ∗/ #i f d e f HAVE SETPGID i f ( s e t p g i d (0 ,0) < 0) r b s y s f a i l (0) ; #e l i f d e f i n e d (HAVE SETPGRP) && d e f i n e d (SETPGRP VOID) i f ( s e t p g r p () < 0) r b s y s f a i l (0) ; #e n d i f return INT2FIX (0) ; } #e n d i f
a program in Ruby def daemonize_app exit if fork Process.setsid exit if fork Dir.chdir("/") STDIN.reopen("/dev/null") STDOUT.reopen("/dev/null", "a") STDERR.reopen("/dev/null", "a") end
$ l s −l / proc /2206/ fd t o t a l 0 lrwx−−−−−− 1 s e l u s e l u 64 Sep 21 16:52 0 −> / dev / n u l l lrwx−−−−−− 1 s e l u s e l u 64 Sep 21 16:52 1 −> / dev / n u l l lrwx−−−−−− 1 s e l u s e l u 64 Sep 21 16:52 2 −> / dev / n u l l l r −x−−−−−− 1 s e l u s e l u 64 Sep 21 16:52 3 −> pipe : [ 5 9 5 6 6 3 ] l −wx−−−−−− 1 s e l u s e l u 64 Sep 21 16:52 4 −> pipe : [ 5 9 5 6 6 3 ] l r −x−−−−−− 1 s e l u s e l u 64 Sep 21 16:52 5 −> pipe : [ 5 9 5 6 6 4 ] l −wx−−−−−− 1 s e l u s e l u 64 Sep 21 16:52 6 −> pipe : [ 5 9 5 6 6 4 ] $ ps x f −o pid , ppid , pgid , sid , command | grep −e [ r ] uby −e [P] ID PID PPID PGID SID COMMAND 2206 1 2203 2203 ruby −e Process . daemon ; s l e e p 3600
gem From https://github.com/ghazel/daemons/blob/master/lib/daemons/daemonize.rb def daemonize ( l o g f i l e n a m e = nil , app name = nil) srand s a f e f o r k and e x i t unless s e s s i d = Process . s e t s i d r a i s e Daemons . RuntimeException . new ( ’ cannot detach from c o n t r o l l i n g t e r m i n a l ’ ) end # Prevent the possibility of acquiring a controlling terminal trap ’SIGHUP ’ , ’IGNORE ’ e x i t if pid = s a f e f o r k $0 = app name if app name Dir . c h d i r ”/” F i l e . umask 0000 ObjectSpace . e a c h o b j e c t ( IO ) do | i o | unless [ STDIN , STDOUT, STDERR ] . i n c l u d e ?( i o ) begin i o . c l o d e unless i o . c l o s e d ? rescue : : Exception end end end r e d i r e c t i o ( l o g f i l e n a m e ) return s e s s i d end
r e q u i r e ’ socket ’ Process . daemon socket = TCPServer . open ( ’ 0 . 0 . 0 . 0 ’ , 8080) wpids = [ ] 5. times do wpids < < f o r k do loop do connection = socket . accept connection . puts ” H e l l o from #{Process . pid}” connection . c l o s e end end end [ : INT , : QUIT ] . each do | s i g n a l | S i g n a l . trap ( s i g n a l ) do wpids . each { | wpid | Process . k i l l ( s i g n a l , wpid ) } end end Process . w a i t a l l $ nc l o c a l h o s t 8080; nc l o c a l h o s t 8080 Hello from 8349 Hello from 8361
handle_signal(signal) puts("Received #{signal}") end self_read, self_write = IO.pipe %w(INT TERM).each do |sig| trap(sig) { self_write.puts(sig) } end while readable_io = IO.select([self_read]) signal = readable_io.first[0].gets.strip handle_signal(signal) end
Process . daemon socket = TCPServer . open ( ’ 0 . 0 . 0 . 0 ’ , 8080) wpids = [ ] 5. times do wpids < < f o r k do run = true [ : INT , : QUIT ] . each do | s i g n a l | S i g n a l . trap ( s i g n a l , lambda { run = false }) end while run connection = socket . accept connection . puts ( ” H e l l o from #{Process . pid}” ) s l e e p 10 connection . puts ( ”Goodbye from #{Process . pid}” ) connection . c l o s e end end end [ : INT , : QUIT ] . each do | s i g n a l | S i g n a l . trap ( s i g n a l ) do wpids . each { | wpid | Process . k i l l ( s i g n a l , wpid ) } end end Process . w a i t a l l $ nc l o c a l h o s t 8080; k i l l a l l −INT ruby Hello from 8328 Goodbye from 8328
with logging Process . daemon socket = TCPServer . open ( ’ 0 . 0 . 0 . 0 ’ , 8080) wpids = [ ] l o g g e r = Logger . new ( ’ /tmp/ l o g g e r . log ’ ) l o g g e r . l e v e l = Logger : : INFO 5 . times do wpids < < f o r k do run = true [ : INT , : QUIT ] . each do | s i g n a l | S i g n a l . trap ( s i g n a l , lambda { run = false }) end while run connection = socket . accept connection . puts ( ” H e l l o from #{Process . pid}” ) l o g g e r . i n f o ( ” Connection i n #{Process . pid}” ) s l e e p 10 connection . puts ( ”Goodbye from #{Process . pid}” ) connection . c l o s e end end end [ : INT , : QUIT ] . each do | s i g n a l | S i g n a l . trap ( s i g n a l ) do wpids . each { | wpid | Process . k i l l ( s i g n a l , wpid ) } end end Process . w a i t a l l l o g g e r . c l o s e $ t a i l −f /tmp/ l o g g e r . log # L o g f i l e c r e a t e d on 2014−09−21 19:46:25 +0200 by l o g g e r . rb /v1 . 2 . 7 I , [2014−09−21T19 :47: 12. 696949 #9452] INFO − − : Connection i n 9452 I , [2014−09−21T19 :47: 22. 702008 #9449] INFO − − : Connection i n 9449
a signal From https://github.com/kennethkalmer/daemon-kit/blob/master/lib/daemon kit/application.rb c o n f i g u r a t i o n . trap ( ”HUP” ) { DaemonKit : : A p p l i c a t i o n . r e o p e n l o g s } module DaemonKit class A p p l i c a t i o n def r e o p e n l o g s nr = 0 a p p e n d f l a g s = F i l e : :WRONLY | F i l e : : APPEND DaemonKit . l o g g e r . i n f o ” Rotating l o g s ” if DaemonKit . l o g g e r ObjectSpace . e a c h o b j e c t ( F i l e ) do | fp | next if fp . c l o s e d ? next unless ( fp . sync && fp . path [ 0 . . 0 ] == ”/” ) next unless ( fp . f c n t l ( F c n t l : : F GETFL) & a p p e n d f l a g s ) == a p p e n d f l a g s begin a , b = fp . stat , F i l e . s t a t ( fp . path ) next if a . ino == b . ino && a . dev == b . dev rescue Errno : : ENOENT end open arg = ’ a ’ if fp . r e s p o n d t o ? ( : e x t e r n a l e n c o d i n g ) && enc = fp . e x t e r n a l e n c o d i n g open arg < < ”:#{enc . t o s}” enc = fp . i n t e r n a l e n c o d i n g and open arg < < ”:#{enc . t o s}” end DaemonKit . l o g g e r . i n f o ” Rotating path : #{fp . path}” if DaemonKit . l o g g e r fp . reopen ( fp . path , open arg ) fp . sync = true nr += 1 end # each_object nr end end end
info: http://codeincomplete.com/posts/2014/9/15/ruby daemons/ Working with unix processes by Jesse Storimer lib/unicorn/launcher.rb in Unicorn gem daemons, dante and daemon-kit gems Linux System Programming: Talking Directly to the Kernel and C Library Understanding the Linux Kernel
info: http://codeincomplete.com/posts/2014/9/15/ruby daemons/ Working with unix processes by Jesse Storimer lib/unicorn/launcher.rb in Unicorn gem daemons, dante and daemon-kit gems Linux System Programming: Talking Directly to the Kernel and C Library Understanding the Linux Kernel Questions?
info: http://codeincomplete.com/posts/2014/9/15/ruby daemons/ Working with unix processes by Jesse Storimer lib/unicorn/launcher.rb in Unicorn gem daemons, dante and daemon-kit gems Linux System Programming: Talking Directly to the Kernel and C Library Understanding the Linux Kernel Questions? Thanks!
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