Why there are some duplicate processes in this fresh installed Debian 7?

jrdai

ps -A

PID TTY TIME CMD
1 ? 00:00:00 init
2 ? 00:00:00 kthreadd/7622
3 ? 00:00:00 khelper/7622
87 ? 00:00:00 upstart-udev-br
98 ? 00:00:00 udevd
141 ? 00:00:00 udevd
143 ? 00:00:00 udevd
236 ? 00:00:00 upstart-socket-
1529 ? 00:00:00 rsyslogd
1574 ? 00:00:00 saslauthd
1576 ? 00:00:00 saslauthd
1641 ? 00:00:00 xinetd
1674 ? 00:00:00 apache2
1677 ? 00:00:00 apache2
1718 ? 00:00:00 cron
1748 ? 00:00:00 sshd
1750 pts/0 00:00:00 bash
1818 ? 00:00:00 sshd
1836 pts/0 00:00:00 ps

netstat -ntpl

Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address Foreign Address State PID/Program name
tcp 0 0 0.0.0.0:22 0.0.0.0:* LISTEN 1818/sshd
tcp 0 0 0.0.0.0:80 0.0.0.0:* LISTEN 1674/apache2

I don't understand why there are 3 udevd, 2 sshd, and 2 saslauthd, 2 apache2?

At first, I thought sshd is listenning to both IPv4 and IPv6, so I turn it IPv4 only, but still, there are two processes. Forgive me if this is a dummy question, I am kinda noob.

neroux

These are most probably forked processes.

nunim

Apache runs as more than one process by default.

You can set the number of servers launched at startup by editing StartServers in the httpd.conf.

craigb

sshd uses privilege separation by default, so you'll see 2 sshd processes for each ssh connection (plus the original sshd daemon process that listens for new ssh connections).

udevd spawns worker threads on startup (in a similar way to apache workers).

you might find the output of pstree -aplu more instructive - it's more visual and shows the relationship and user transitions of processes