Tag Archives: Ubuntu

Replacing Sendmail with Postfix on Ubuntu causes error postdrop: warning: unable to look up public/pickup: No such file or directory

On one of our machines the original Sysadmin had setup Sendmail, but on all our other machines the default version installed by Ubuntu is Postfix.  Rather than having to maintain and troubleshoot several type of systems, I wanted the sendmail one to be changed to match our Postfix systems.

The advice at this forum post which said to simply apt-get install postfix and it would automatically remove Sendmail.  Which it did.  Goes into the postfix screen and I set it up as per usual.  However, when testing it out from the command line by trying to send a logwatch report, I get this error:

postdrop: warning: unable to look up public/pickup: No such file or directory

Thanks to this article at databasically.com I found out that Ubuntu wasn’t removing sendmail completely, in fact it wasn’t stopping the sendmail process!  Here’s the solution that was posted:

mkfifo /var/spool/postfix/public/pickup
ps aux | grep mail
kill [insert process number]
sudo /etc/init.d/postfix restart

PHP APC config syntax causes [apc-error] apc_mmap: mmap failed: Invalid argument

After upgrading Ubuntu server from 9.10 to 10.04LTS PHP’s APC cache wasn’t functioning.  Apache wouldn’t start, it hung in the process list and printed this error to /var/log/apache2/error.log

[apc-error] apc_mmap: mmap failed: Invalid argument

The apache process would show up in the process like this:

apc@hostaname# ps aux | grep apache
www-data 6958 104 0.0 139044 3624 ? R 12:47 0:19 /usr/sbin/apache2 -k start

This process would then have to be killed, APC commented out, and then the web server restarted just to continue on without APC until a solution was found.

The PHP manual states this regarding MMAP support in APC:

http://php.net/manual/en/apc.configuration.php

When APC is compiled with mmap support (Memory Mapping), it will use only one memory segment, unlike when APC is built with SHM (SysV Shared Memory) support that uses multiple memory segments. MMAP does not have a maximum limit like SHM does in /proc/sys/kernel/shmmax. In general MMAP support is recommeded because it will reclaim the memory faster when the webserver is restarted and all in all reduces memory allocation impact at startup.

APC was made to run by commenting out all lines from the PHP config file except for:

extension=apc.so
apc.enabled = 1

This config can exist in a number of places. In 9.10 APC had been compiled by PECL so it was in our /etc/php5/apache2/php.ini file. However, in 10.04 APC is a package so we removed the PECL version, installed the version using apt-get install php-apc and moved the configuration to /etc/php5/conf.d/apc.ini for better consistency.

pear uninstall apc
apt-get install php-apc

As I began to uncomment lines one by one, it turned out the culprit was in the apc.shm_size directive. The default size is 30M, but as soon as the directive was uncommented it crashed Apache. I was unable to specify any value at all, even the same or lesser value. I even tried with quotes and removing quotes. That’s when I started thinking syntax may be a problem because it works when using the default value (shm_size commented out) but fails with an “invalid argument” error. That makes me think APC is sending an invalid argument to MMAP. In which case I find this post that confirms my suspicion.

http://stackoverflow.com/questions/6716929/apc-configuration-on-ubuntu-10-4-problem-with-apc-shm-size-apc-shm-segments-an

It turns out that the “M” for Megabytes cannot be specified in the shm_size directive for APC in Ubuntu server 10.04 because it is using APC version 3.1.3p1. However, on 9.10 APC wasn’t included as a package so it was installed with PEAR PECL which installed a more recent version of APC (3.1.9) which did allow specifying the “M” in the shm_size directive.

If you wish this to work in your config file, it should read like this in older versions of APC:

apc.shm_size = 100

This would specify 100M shared memory segments, and would be equivalent to this in newer versions:

apc.shm_size = 100M

And you can also put quotees around the “100M” if you like.

After these changes I had Apache up and running again, the APC cache helping PHP along, and some of the quickest loading pages I’ve seen in a while.

Mounting NFS causes error “mount: wrong fs type, bad option, bad superblock on …”

Some days the obvious just passes you by.

On a fresh install of Ubuntu server I found that trying to mount an NFS export from our NAS wouldn’t complete. I had the correct options in /etc/fstab on this machine and in /etc/exports on the NFS server as evidence by the success of other machines connected to it. Mounting it on this server gave the following error:

root@iknow:/var/log# mount /mnt/backup
mount: wrong fs type, bad option, bad superblock on 10.20.30.40:/mnt/my_backup,
missing codepage or helper program, or other error
(for several filesystems (e.g. nfs, cifs) you might
need a /sbin/mount. helper program)
In some cases useful info is found in syslog - try
dmesg | tail or so

After double checking everything several times the light bulb finally came on. nfs-common wasn’t installed!

sudo apt-get install nfs-common

It installed, I retried the mount, and it succeeded. Just remember that as a client, you have to have nfs-common installed if you want to mount an NFS export from the server.

Echo Layla Working in Ubuntu Linux

The Echo pro audio products are great. I’ve been using an Echo Layla 24/96 since about 2002. I primarily do my recording with 64Studio, but I like to listen to music while I work on programming in Ubuntu.

I haven’t had problems getting it working in most versions of Linux for the last few years. Easiest install was recognized right off the bat by Mandriva. My memory doesn’t serve me too well, but 64Studio works flawlessly with record low latencies.

But it didn’t’ work right out of the box with Ubuntu, and that’s no big deal. Finding out how to get it to work was tougher. Lot’s of people complaining that Linux doesn’t “just work.” Well, when I installed Layla on Windows it didn’t just work either, I had to install a driver. Fortunately in Linux the driver is already included. What’s missing is the mixer and firmware.

It’s too bad but there are many solutions out there including compiling ALSA from scratch. But the solution I found over at the Echo forums was much, much simpler. Here’s the excerpt from I want to use Layla 3g in Ubuntu

1) Add the Medibuntu (https://help.ubuntu.com/community/Medibuntu) repository to your software sources.
2) Install the alsa-firmware package to get the drivers.
3) Install alsa-tools-gui package to get echomixer (a mixer for Echo Audio cards).
4) If you’re using PulseAudio you need to manually add it to your /etc/pulse/default.pa file *.
5) Reboot & enjoy high quality sound.

And that worked for me. Make sure after you reboot to have your volume down low on your speakers, then after it starts up load the echomixer program from your Sound menu, and adjust it properly.

No problem. You should have your Echo Layla, Layla24, and possibly 3g, Mia, Gina and other Echo pro audio cards working in Linux.