init: Id "co" respawning too fast: disabled for 5 minutes

From Linux syslog (i.e., /var/log/messages), we have found the following repeated messages:

• Dec 17 04:21:41 myserver init: Id "co" respawning too fast: disabled for 5 minutes

As usual, we have taken action to investigate it.  Here is the report on what we have found.

The Culprit

The serial ports^[2] in Linux are named ttyS0, ttyS1, etc. The /dev directory has a special file for each port. Type "ls /dev/ttyS*" to see them. Just because there may be (for example) a ttyS1 file, doesn't necessarily mean that there exists a physical serial port there.

For our issue, it turns out to be:

• ttyS1 physical serial port is not present on our host myserer

To find out if a physical serial port is present or not, you can test it in two ways:

1. Using setserial command
2. Using dmesg command

Output from setserial Command

As shown below, we can tell that ttyS0 is present, but not ttyS1:

[aroot@myserver oracle]# setserial /dev/ttyS0
/dev/ttyS0, UART: 16550A, Port: 0x03f8, IRQ: 4
[aroot@myserver oracle]# setserial /dev/ttyS1
/dev/ttyS1, UART: unknown, Port: 0x02f8, IRQ: 3

Output from dmesg Command

As shown below, only ttyS0 is printed by dmesg:

[root@myserver ~]# dmesg | grep tty
serial8250: ttyS0 at I/O 0x3f8 (irq = 4) is a 16550A
00:05: ttyS0 at I/O 0x3f8 (irq = 4) is a 16550A

The Solution

Because ttyS1 is absent, that is why the following line in /etc/inittab is failing and causes the re-spawning:

• co:2345:respawn:/sbin/agetty 9600 ttyS1

When a process re-spawns too many times, it will be disabled for sometime by the kernel to keep the host stable. Following message is the result of that:

• init: Id "co" respawning too fast: disabled for 5 minutes

As there is no ttyS1, the fix for our issue is:

1. $su aroot
2. #vi /etc/inittab
   • Commenting or removing the line for co
3. #init q

You can verify that inittab is re-read by Linux kernel from the following line:

• Dec 17 23:49:40 myserver init: Re-reading inittab

in Linux syslog.

References

1. INIT: id "co" respawning too fast: disabled for 5 minutes
2. Linux Serial How-To