Best of Technical Support
I would like to know what can be said about viruses in a Linux system which is installed on the same hard disk as Win95. For example, what can happen if a virus infects the MBR sector (where resides LILO) or if I mount an infected MS-DOS formatted diskette?
Leaving out the usual statements about Unix systems being immune to standard virus attacks, this is an important point most people should consider, since many people who run Linux on personal computers (as opposed to servers) also run Win95 or some other operating system. You should be safe from a mounted floppy, but be warned that you can get some very odd effects reading such a disk, such as strange directory entries.
There are several scenarios, from boot sector infection to random pot shots some viruses are known to take. Unlike the DOS file systems, which concentrate their layout information into one or two dense tables, Linux spreads these across the disk. Random potshots are much more likely to wipe out vital structures on a Linux disk than they are on a DOS disk (assuming the virus ran from a booted DOS system).
Safety first, as always. When in Unix, don't use the root user account unless you need to. Create a normal user account in which to do your work. When in DOS, scan—scan—scan.
—Chad Robinson, BRT Technologies Senior System Analyst firstname.lastname@example.org
Chances are that if your system becomes infected with a boot sector virus, LILO will no longer work. The best defense against this situation is to keep an emergency boot floppy handy. I generally create them using the command dd if=/vmlinuz of=/dev/fd0. You will want to write-protect it of course. After booting from floppy, simply re-run LILO. Assuming you have LILO configured to use the system MBR, it will overwrite the virus.
The Linux operating system itself is not very vulnerable to MS-DOS-style viruses. All of the common ones depend on being in a DOS/Windows environment. They do not know how to cope with Linux and do not function.
—Keith Stevenson email@example.com
I have been working with the Linux system for almost two years. My problem is memory allocation. The kernel (2.xx) does not reclaim memory after things such as X sessions are perfomed. I am constantly rebooting the machine (shutdown -r now) in order to gain sufficient memory for multiple operations. Is there an executable that can be run which will free all possible memory that current kernel processes are not using?
If the answer is no, then how can one use Linux as an httpd server that takes a lot of hits per day? The system would almost always be short of memory to be able to quickly service, multiple httpd server and other processes. In short, I am somewhat disappointed in the way Linux handles memory reclamation. Is it that the X Server and applications are simply “poorly written” and do not free memory upon exit?
—George R. Boyko
There are no memory leakages in Linux 2.0; there may be some in the 2.1 kernel series, but those versions are only beta-releases aimed specifically at developers. It's true, on the other hand, that the amount of free memory reported by a running Linux system is always tiny. This is a feature rather than a bug; free memory is just wasted, and Linux tries to avoid any waste by keeping disk buffers and page caches in an otherwise waste-free memory.
It's the kernel which releases any process resources upon exit. You don't want your students to lock memory by not calling free, do you? As a matter of fact, many one-shot programs are “poorly written” and rely on the system to close files and release memory.
—Alessandro Rubini firstname.lastname@example.org
Memory management is one of the things I really like about Linux. I find it to be much more efficient than a certain popular commercial OS.
I have several Linux systems, all with 64MB of installed RAM. I use xosview to monitor things like CPU activity and memory utilization. These machines function as ftp servers, web servers and multi-user workstations. According to xosview, the memory utilization is consistently above 90% even when the machine is lightly loaded. This isn't a problem. It simply means that there is a lot of stuff cached in memory. The real indicator of whether or not you have enough RAM in your system is swap space utilization. This can be monitored with xosview or with the command vmstat. If you are swapping to disk often, you probably need to add more RAM to the system. If not, then things are probably okay. My 64MB systems almost never swap out to disk, and they have excellent response time despite the fact that 90% or more of their RAM is marked as being “in use”.
—Keith Stevenson email@example.com
Practical Task Scheduling Deployment
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.
Join Linux Journal's Mike Diehl and Pat Cameron of Help Systems.
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|The Firebird Project's Firebird Relational Database||Jul 29, 2016|
|Stunnel Security for Oracle||Jul 28, 2016|
|SUSE LLC's SUSE Manager||Jul 21, 2016|
|My +1 Sword of Productivity||Jul 20, 2016|
|Non-Linux FOSS: Caffeine!||Jul 19, 2016|
|Murat Yener and Onur Dundar's Expert Android Studio (Wrox)||Jul 18, 2016|
- The Firebird Project's Firebird Relational Database
- Stunnel Security for Oracle
- My +1 Sword of Productivity
- Non-Linux FOSS: Caffeine!
- Managing Linux Using Puppet
- SUSE LLC's SUSE Manager
- Murat Yener and Onur Dundar's Expert Android Studio (Wrox)
- Doing for User Space What We Did for Kernel Space
- Google's SwiftShader Released
- SuperTuxKart 0.9.2 Released
With all the industry talk about the benefits of Linux on Power and all the performance advantages offered by its open architecture, you may be considering a move in that direction. If you are thinking about analytics, big data and cloud computing, you would be right to evaluate Power. The idea of using commodity x86 hardware and replacing it every three years is an outdated cost model. It doesn’t consider the total cost of ownership, and it doesn’t consider the advantage of real processing power, high-availability and multithreading like a demon.
This ebook takes a look at some of the practical applications of the Linux on Power platform and ways you might bring all the performance power of this open architecture to bear for your organization. There are no smoke and mirrors here—just hard, cold, empirical evidence provided by independent sources. I also consider some innovative ways Linux on Power will be used in the future.Get the Guide