Best of Technical Support
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
Are you sure your automail program is executable? If it isn't, type:
chmod +x /home/Talon/automail
—Pierre Ficheux, Lectra Systèmès firstname.lastname@example.org
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
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 email@example.com
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
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 firstname.lastname@example.org
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
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:
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 email@example.com
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
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 firstname.lastname@example.org
Practical Task Scheduling Deployment
July 20, 2016 12:00 pm CDT
One of the best things about the UNIX environment (aside from being stable and efficient) is the vast array of software tools available to help you do your job. Traditionally, a UNIX tool does only one thing, but does that one thing very well. For example, grep is very easy to use and can search vast amounts of data quickly. The find tool can find a particular file or files based on all kinds of criteria. It's pretty easy to string these tools together to build even more powerful tools, such as a tool that finds all of the .log files in the /home directory and searches each one for a particular entry. This erector-set mentality allows UNIX system administrators to seem to always have the right tool for the job.
Cron traditionally has been considered another such a tool for job scheduling, but is it enough? This webinar considers that very question. The first part builds on a previous Geek Guide, Beyond Cron, and briefly describes how to know when it might be time to consider upgrading your job scheduling infrastructure. The second part presents an actual planning and implementation framework.
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