5. System Strategies for Small and Read Only Environments

In Section 3, “The rc Subsystem and Read-Only Filesystems”, it was pointed out that the /var filesystem constructed by /etc/rc.d/var and the presence of a read-only root filesystem causes problems with many common software packages used with FreeBSD. In this article, suggestions for successfully running cron, syslog, ports installations, and the Apache web server will be provided.

5.1. Cron

Upon boot, /var gets populated by /etc/rc.d/var using the list from /etc/mtree/BSD.var.dist, so the cron, cron/tabs, at, and a few other standard directories get created.

However, this does not solve the problem of maintaining cron tabs across reboots. When the system reboots, the /var filesystem that is in memory will disappear and any cron tabs you may have had in it will also disappear. Therefore, one solution would be to create cron tabs for the users that need them, mount your / filesystem as read-write and copy those cron tabs to somewhere safe, like /etc/tabs, then add a line to the end of /etc/rc.initdiskless that copies those crontabs into /var/cron/tabs after that directory has been created during system initialization. You may also need to add a line that changes modes and permissions on the directories you create and the files you copy with /etc/rc.initdiskless.

5.2. Syslog

syslog.conf specifies the locations of certain log files that exist in /var/log. These files are not created by /etc/rc.d/var upon system initialization. Therefore, somewhere in /etc/rc.d/var, after the section that creates the directories in /var, you will need to add something like this:

# touch /var/log/security /var/log/maillog /var/log/cron /var/log/messages
# chmod 0644 /var/log/*

5.3. Ports Installation

Before discussing the changes necessary to successfully use the ports tree, a reminder is necessary regarding the read-only nature of your filesystems on the flash media. Since they are read-only, you will need to temporarily mount them read-write using the mount syntax shown in Section 3, “The rc Subsystem and Read-Only Filesystems”. You should always remount those filesystems read-only when you are done with any maintenance - unnecessary writes to the flash media could considerably shorten its lifespan.

To make it possible to enter a ports directory and successfully run make install, we must create a packages directory on a non-memory filesystem that will keep track of our packages across reboots. As it is necessary to mount your filesystems as read-write for the installation of a package anyway, it is sensible to assume that an area on the flash media can also be used for package information to be written to.

First, create a package database directory. This is normally in /var/db/pkg, but we cannot place it there as it will disappear every time the system is booted.

# mkdir /etc/pkg

Now, add a line to /etc/rc.d/var that links the /etc/pkg directory to /var/db/pkg. An example:

# ln -s /etc/pkg /var/db/pkg

Now, any time that you mount your filesystems as read-write and install a package, the make install will work, and package information will be written successfully to /etc/pkg (because the filesystem will, at that time, be mounted read-write) which will always be available to the operating system as /var/db/pkg.

5.4. Apache Web Server


The steps in this section are only necessary if Apache is set up to write its pid or log information outside of /var. By default, Apache keeps its pid file in /var/run/httpd.pid and its log files in /var/log.

It is now assumed that Apache keeps its log files in a directory apache_log_dir outside of /var. When this directory lives on a read-only filesystem, Apache will not be able to save any log files, and may have problems working. If so, it is necessary to add a new directory to the list of directories in /etc/rc.d/var to create in /var, and to link apache_log_dir to /var/log/apache. It is also necessary to set permissions and ownership on this new directory.

First, add the directory log/apache to the list of directories to be created in /etc/rc.d/var.

Second, add these commands to /etc/rc.d/var after the directory creation section:

# chmod 0774 /var/log/apache
# chown nobody:nobody /var/log/apache

Finally, remove the existing apache_log_dir directory, and replace it with a link:

# rm -rf apache_log_dir
# ln -s /var/log/apache apache_log_dir

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