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Linux/Making Linux Daemon

사전 지식

root@zeropage:~# ps -efjc
UID        PID  PPID  PGID   SID CLS PRI STIME TTY          TIME CMD
root         1     0     0     0 TS   23 Oct15 ?        00:00:00 init [2]         
root         2     1     0     0 TS    5 Oct15 ?        00:00:00 [ksoftirqd/0]
root         3     1     0     0 TS   29 Oct15 ?        00:00:00 [events/0]
root         4     1     0     0 TS   28 Oct15 ?        00:00:00 [khelper]
root         5     1     0     0 TS   23 Oct15 ?        00:00:00 [kthread]
root         7     5     0     0 TS   19 Oct15 ?        00:00:00 [kacpid]
root        60     5     0     0 TS   29 Oct15 ?        00:00:00 [kblockd/0]
root        86     5     0     0 TS   24 Oct15 ?        00:00:00 [pdflush]
root        87     5     0     0 TS   24 Oct15 ?        00:00:00 [pdflush]
root        89     5     0     0 TS   22 Oct15 ?        00:00:00 [aio/0]
root        88     1     1     1 TS   24 Oct15 ?        00:00:01 [kswapd0]
root       674     1     1     1 TS   22 Oct15 ?        00:00:00 [kseriod]
root       943     1     1     1 TS   24 Oct15 ?        00:00:00 [kjournald]
root      1095     1     1     1 TS   24 Oct15 ?        00:00:01 [kjournald]
root      1096     1     1     1 TS   24 Oct15 ?        00:00:02 [kjournald]
root      1097     1     1     1 TS   24 Oct15 ?        00:00:00 [kjournald]
root      1098     1     1     1 TS   24 Oct15 ?        00:00:01 [kjournald]
root      1099     1     1     1 TS   24 Oct15 ?        00:00:00 [kjournald]
daemon    1191     1  1191  1191 TS   22 Oct15 ?        00:00:00 /sbin/portmap
root      1314     1  1313  1313 TS   24 Oct15 ?        00:00:00 /usr/sbin/syslogd
bind      1323     1  1323  1323 TS   21 Oct15 ?        00:00:00 /usr/sbin/named -u bind
105       1334     1  1334  1334 TS   21 Oct15 ?        00:00:00 /usr/bin/dbus-daemon-1 --system
104       1366     1  1366  1366 TS   23 Oct15 ?        00:00:00 /usr/sbin/exim4 -bd -q30m
root      1372     1  1371  1371 TS   18 Oct15 ?        00:00:00 /usr/sbin/inetutils-inetd
root      1387     1  1303  1303 TS   14 Oct15 ?        00:00:00 /bin/sh /usr/bin/mysqld_safe
root      1417  1387  1303  1303 TS   14 Oct15 ?        00:00:00 /bin/sh /usr/bin/mysqld_safe
mysql     1418  1417  1303  1303 TS   23 Oct15 ?        00:06:23 /usr/sbin/mysqld --basedir=/usr --datad
root      1419  1417  1303  1303 TS   23 Oct15 ?        00:00:00 logger -p daemon.err -t mysqld_safe -i
root      1461     1  1461  1461 TS   24 Oct15 ?        00:00:00 /usr/sbin/sshd
root      1475     1  1303  1303 TS   14 Oct15 ?        00:03:00 /usr/local/jdk/jre/bin/java -Djava.util
root      1481     1  1481  1481 TS   23 Oct15 ?        00:00:00 /usr/sbin/vsftpd
root      1485     1  1485  1485 TS   21 Oct15 ?        00:00:00 /usr/sbin/famd -T 0
daemon    1497     1  1497  1497 TS   23 Oct15 ?        00:00:00 /usr/sbin/atd
root      1500     1  1500  1500 TS   23 Oct15 ?        00:00:00 /usr/sbin/cron
root      1538     1  1538  1538 TS   23 Oct15 tty1     00:00:00 /sbin/getty 38400 tty1
root      1540     1  1540  1540 TS   23 Oct15 tty2     00:00:00 /sbin/getty 38400 tty2
root      1541     1  1541  1541 TS   23 Oct15 tty3     00:00:00 /sbin/getty 38400 tty3
root      1542     1  1542  1542 TS   23 Oct15 tty4     00:00:00 /sbin/getty 38400 tty4
root      1543     1  1543  1543 TS   23 Oct15 tty5     00:00:00 /sbin/getty 38400 tty5
root      1544     1  1544  1544 TS   23 Oct15 tty6     00:00:00 /sbin/getty 38400 tty6
root      5722     1  5722  5722 TS   23 Oct16 ?        00:00:01 /usr/sbin/apache2 -k start -DSSL
www-data  5724  5722  5722  5722 TS   23 Oct16 ?        00:00:00 /usr/sbin/fcgi-pm -k start -DSSL
www-data 11061  5722  5722  5722 TS   24 22:30 ?        00:00:01 /usr/sbin/apache2 -k start -DSSL
www-data 11123  5722  5722  5722 TS   22 22:54 ?        00:00:04 /usr/sbin/apache2 -k start -DSSL
www-data 11184  5722  5722  5722 TS   23 23:05 ?        00:00:02 /usr/sbin/apache2 -k start -DSSL
www-data 11360  5722  5722  5722 TS   23 23:30 ?        00:00:00 /usr/sbin/apache2 -k start -DSSL
www-data 11392  5722  5722  5722 TS   20 23:32 ?        00:00:03 /usr/sbin/apache2 -k start -DSSL
www-data 11393  5722  5722  5722 TS   23 23:32 ?        00:00:00 /usr/sbin/apache2 -k start -DSSL
www-data 11394  5722  5722  5722 TS   23 23:32 ?        00:00:00 /usr/sbin/apache2 -k start -DSSL
www-data 11395  5722  5722  5722 TS   24 23:32 ?        00:00:00 /usr/sbin/apache2 -k start -DSSL
www-data 11396  5722  5722  5722 TS   23 23:32 ?        00:00:00 /usr/sbin/apache2 -k start -DSSL
www-data 11397  5722  5722  5722 TS   23 23:32 ?        00:00:00 /usr/sbin/apache2 -k start -DSSL
root     11434  1461 11434 11434 TS   24 23:41 ?        00:00:00 sshd: sapius@pts/0
root     11436 11434 11436 11436 TS   24 23:41 pts/0    00:00:00 -bash
root     11453 11436 11453 11436 TS   22 23:41 pts/0    00:00:00 ps -efjc
상기에서 확인가능 하듯 daemon 으로 동작하는 프로그램은 터미널이 할당되지 않는다. 또한 기본적으로 ParentPID (ProcessID)가 1번으로 설정되어있음을 알 수 있다. 이는 1번 PID를 가진 init 프로세스가 데몬의 동작을 관리한다는 사실을 알 수 있게 한다.

사전지식

PPID 가 1인 프로세스를 작성하기 위해서 지켜야할 rule
1. fork 호출하여 자식 프로세스 생성. 부모프로세스 종료
2. setsid 이용 새로운 세션 생성, 현재 프로세스의 PID가 세션 제어권을 가지도록 설정
3. chdir 프로세스가 루트에서 작업하도록 변경
1 부연설명
자식의 프로세스가 종료되기 전에 부모 프로세스가 종료되면 자식의 PPID는 1번 PID로 설정된다.
2 부연설명
새로운 세션을 만든다. 일반적으로 tty 를 부여해야하지만, 부여하지 않을 경우 터미널이 없는 세션으로 생성된다.
3 부연설명
상대경로 지정으로 일어나는 프로그램내의 문제해결 (안해도 무관)

sample code

~cpp
#include <sys/types.h> 
#include <sys/stat.h> 
#include <stdio.h> 
#include <fcntl.h> 

int main()
{
    pid_t   pid;

    if (( pid = fork()) < 0)
    exit(0);

    // 부모프로세스를 종료한다. 
    else if(pid != 0)
    exit(0);
    
    //setsid();
    chdir("/");

    // 여기에 프로그램 본체를 넣는다. 
    setsid();    
    while(1)
    {
    sleep(1);
    }
}

result

root@zeropage:~# ps -ejfc
UID        PID  PPID  PGID   SID CLS PRI STIME TTY          TIME CMD
root         1     0     0     0 TS   23 Oct15 ?        00:00:00 init [2]         
root         2     1     0     0 TS    5 Oct15 ?        00:00:00 [ksoftirqd/0]
root         3     1     0     0 TS   29 Oct15 ?        00:00:00 [events/0]
root         4     1     0     0 TS   28 Oct15 ?        00:00:00 [khelper]
root         5     1     0     0 TS   23 Oct15 ?        00:00:00 [kthread]
root         7     5     0     0 TS   19 Oct15 ?        00:00:00 [kacpid]
root        60     5     0     0 TS   29 Oct15 ?        00:00:00 [kblockd/0]
root        86     5     0     0 TS   24 Oct15 ?        00:00:00 [pdflush]
root        87     5     0     0 TS   24 Oct15 ?        00:00:00 [pdflush]
root        89     5     0     0 TS   22 Oct15 ?        00:00:00 [aio/0]
root        88     1     1     1 TS   24 Oct15 ?        00:00:01 [kswapd0]
root       674     1     1     1 TS   22 Oct15 ?        00:00:00 [kseriod]
root       943     1     1     1 TS   24 Oct15 ?        00:00:00 [kjournald]
root      1095     1     1     1 TS   24 Oct15 ?        00:00:01 [kjournald]
root      1096     1     1     1 TS   23 Oct15 ?        00:00:02 [kjournald]
root      1097     1     1     1 TS   24 Oct15 ?        00:00:00 [kjournald]
root      1098     1     1     1 TS   24 Oct15 ?        00:00:01 [kjournald]
root      1099     1     1     1 TS   24 Oct15 ?        00:00:00 [kjournald]
daemon    1191     1  1191  1191 TS   22 Oct15 ?        00:00:00 /sbin/portmap
root      1314     1  1313  1313 TS   23 Oct15 ?        00:00:00 /usr/sbin/syslogd
bind      1323     1  1323  1323 TS   21 Oct15 ?        00:00:00 /usr/sbin/named -u bind
105       1334     1  1334  1334 TS   21 Oct15 ?        00:00:00 /usr/bin/dbus-daemon-1 --system
104       1366     1  1366  1366 TS   23 Oct15 ?        00:00:00 /usr/sbin/exim4 -bd -q30m
root      1372     1  1371  1371 TS   18 Oct15 ?        00:00:00 /usr/sbin/inetutils-inetd
root      1387     1  1303  1303 TS   14 Oct15 ?        00:00:00 /bin/sh /usr/bin/mysqld_safe
root      1417  1387  1303  1303 TS   14 Oct15 ?        00:00:00 /bin/sh /usr/bin/mysqld_safe
mysql     1418  1417  1303  1303 TS   24 Oct15 ?        00:06:23 /usr/sbin/mysqld --basedir=/usr --datad
root      1419  1417  1303  1303 TS   23 Oct15 ?        00:00:00 logger -p daemon.err -t mysqld_safe -i
root      1461     1  1461  1461 TS   24 Oct15 ?        00:00:00 /usr/sbin/sshd
root      1475     1  1303  1303 TS   14 Oct15 ?        00:03:01 /usr/local/jdk/jre/bin/java -Djava.util
root      1481     1  1481  1481 TS   23 Oct15 ?        00:00:00 /usr/sbin/vsftpd
root      1485     1  1485  1485 TS   21 Oct15 ?        00:00:00 /usr/sbin/famd -T 0
daemon    1497     1  1497  1497 TS   23 Oct15 ?        00:00:00 /usr/sbin/atd
root      1500     1  1500  1500 TS   23 Oct15 ?        00:00:00 /usr/sbin/cron
root      1538     1  1538  1538 TS   23 Oct15 tty1     00:00:00 /sbin/getty 38400 tty1
root      1540     1  1540  1540 TS   23 Oct15 tty2     00:00:00 /sbin/getty 38400 tty2
root      1541     1  1541  1541 TS   23 Oct15 tty3     00:00:00 /sbin/getty 38400 tty3
root      1542     1  1542  1542 TS   23 Oct15 tty4     00:00:00 /sbin/getty 38400 tty4
root      1543     1  1543  1543 TS   23 Oct15 tty5     00:00:00 /sbin/getty 38400 tty5
root      1544     1  1544  1544 TS   23 Oct15 tty6     00:00:00 /sbin/getty 38400 tty6
root      5722     1  5722  5722 TS   23 Oct16 ?        00:00:01 /usr/sbin/apache2 -k start -DSSL
www-data  5724  5722  5722  5722 TS   23 Oct16 ?        00:00:00 /usr/sbin/fcgi-pm -k start -DSSL
www-data 11061  5722  5722  5722 TS   23 22:30 ?        00:00:01 /usr/sbin/apache2 -k start -DSSL
www-data 11123  5722  5722  5722 TS   23 22:54 ?        00:00:05 /usr/sbin/apache2 -k start -DSSL
www-data 11184  5722  5722  5722 TS   23 23:05 ?        00:00:02 /usr/sbin/apache2 -k start -DSSL
www-data 11360  5722  5722  5722 TS   23 23:30 ?        00:00:00 /usr/sbin/apache2 -k start -DSSL
www-data 11392  5722  5722  5722 TS   23 23:32 ?        00:00:04 /usr/sbin/apache2 -k start -DSSL
www-data 11394  5722  5722  5722 TS   23 23:32 ?        00:00:00 /usr/sbin/apache2 -k start -DSSL
www-data 11395  5722  5722  5722 TS   23 23:32 ?        00:00:01 /usr/sbin/apache2 -k start -DSSL
www-data 11396  5722  5722  5722 TS   23 23:32 ?        00:00:00 /usr/sbin/apache2 -k start -DSSL
www-data 11397  5722  5722  5722 TS   23 23:32 ?        00:00:00 /usr/sbin/apache2 -k start -DSSL
root     11434  1461 11434 11434 TS   23 23:41 ?        00:00:00 sshd: sapius@pts/0
root     11436 11434 11436 11436 TS   24 23:41 pts/0    00:00:00 -bash
'''root     11503     1 11503 11503 TS   23 23:49 ?        00:00:00 ./test'''
www-data 11508  5722  5722  5722 TS   23 23:50 ?        00:00:00 /usr/sbin/apache2 -k start -DSSL
www-data 11509  5722  5722  5722 TS   23 23:50 ?        00:00:00 /usr/sbin/apache2 -k start -DSSL
www-data 11511  5722  5722  5722 TS   24 23:50 ?        00:00:00 /usr/sbin/apache2 -k start -DSSL
root     11521 11436 11521 11436 TS   23 23:50 pts/0    00:00:00 ps -ejfc
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