Best of Technical Support

Our experts answer your technical questions.
Trouble With crontab

I'm having trouble using the crontab file. This is the first time I have tried it and have not been able to get it working. The daemon crond is running. In my crontab file I have the following line:

30 6 * * * /home/Talon/automail

automail is a shell script to log on to my Internet provider, get my mail and log off. As far as I can tell crond never executes this command. —Jeff Largent

Making Programs Executable

Are you sure your automail program is executable? If it isn't, type:

chmod +x /home/Talon/automail

—Pierre Ficheux, Lectra Systèmès

/dev/fd0 Error Message

When I try to mount /dev/fd0 I get the following error message:

/dev/fd0 is not a block device

What does that mean and how do I fix it? I can fdformat a floppy, but I can't mount or create a file system on one. —Scott Petinga

Identifying Block Devices

Check out the type of /dev/fd0—it should be a block device. If it is properly identified, the leading character for this device in the directory list will be a b. For example:

$ ls -l /dev/fd0
brwxrwxrwx   1 root    floppy     2,    0 Jul 18  1994 /dev/fd0

If the b is not present, re-create the device by typing:

rm /dev/fd0
mknod /dev/fd0 b 2 0
—Pierre Ficheux, Lectra Systèmès

Mysterious Zombie Process

Every time I start up the X program netcfg, it generates a zombie process. I haven't been able to get rid of it. Nobody in my dorm can figure this out either. —Scott

Bug Fixes in netcfg

netcfg is a python script that Red Hat created to ease the configuration of network parameters. This script has been expanded and had many bugs fixed since 4.1 was released.

I suggest you upgrade to the latest netcfg-rpm (which is netcfg-2.15-1.i386.rpm as of this writing). —Mario de Mello Bittencourt Neto, Argo Internet

Limiting Directory Size

How do I limit the size of a directory? I want to limit each customer's directory to 1MB. If a customer attempts to upload 2MB of content via ftp, I want Linux to reject the attempt to store more than 1MB. How do I accomplish this disk management feat? —M. Lamberson

Install Quota Support

This is easy. Install the quota support that will allow you to control the maximum size of a user's home directory. Assuming that you have FTP configured to redirect non-anonymous FTP logins to the actual home directory, it is simply a matter of configuring quota support in your kernel. Just go to /usr/src/linux and type:

make menuconfig

Under the Filesystems entry, check for quota support. Recompile the kernel, reboot and you can configure quota as you wish. —Mario de Mello Bittencourt Neto, Argo Internet

init Run Levels

What do the different run levels listed by the init command do? I have looked in various Unix books and also in Linux Configuration and Installation, but I can't find any information. —Paul Sutton

Different Levels of Operation

A Unix run level is a state of system configuration. Each level signifies a certain level of operation. The run levels are controlled (and are relevant to) the init daemon, which is the first process that is executed when any Unix system is first loaded.

init's job is to start and stop processes, and the run levels help determine which to control. The file /etc/inittab contains entries that init uses to decide which processes to start and how to start them. An entry looks like this:


NM is a two-letter identifier for the command—each command must have its own, unique identifier. LEVs is a list of levels during which to run the command. It is typically a number or set of numbers from 0-5 but can also be an S or even nothing, depending on your version of init. WHEN_AND_HOW is an option specifying when the command should be run, whether init should wait for it to finish or not, whether it should be restarted when it dies and so on. COMMAND is the full path and file name of the command to execute.

The run level corresponds to the LEVs list. For example, the following lines are in my inittab file:

# Start the local dial-in services
s0:45:respawn:/usr/local/sbin/mgetty ttyS0 \
        vt100 -D -x 0
s1:45:respawn:/usr/local/sbin/mgetty ttyS2 \
        vt100 -D -x 0

I have defined two processes, s0 and s1, which will be executed any time the system is in run levels 4 or 5. The respawn option tells init to re-execute the command when the command terminates. (This allows my dial-in lines to accept the new callers when users hang up.) Finally, you can see the command that is run for each entry.

By using run levels, a system administrator can configure a system to automatically start and stop certain processes when they put their systems into different run levels. The most common use for this capability is to have a normal, multi-user level and a single-user administration level. By triggering this level, they can have their servers automatically terminate user processes and disable network support in order to administer their systems.

You can get more information on Unix run levels from the INIT(8) and INITTAB(5) man pages. Since many different Unix flavors exist, there are also many different versions of init. So, you should examine your man pages for exact details. —Chad Robinson, BRT Technical Services Corporation


Free Dummies Books
Continuous Engineering


  • What continuous engineering is
  • How to continuously improve complex product designs
  • How to anticipate and respond to markets and clients
  • How to get the most out of your engineering resources

Get your free book now

Sponsored by IBM

Free Dummies Books
Service Virtualization

Learn to:

  • Define service virtualization
  • Select the most beneficial services to virtualize
  • Improve your traditional approach to testing
  • Deliver higher-quality software faster

Get your free book now

Sponsored by IBM