Linux Community Magazine

Linux computers are put out like any other technical device to possible abuse. While the abuse is not to be avoided by an attacker with direct access to the hardware, abusive accesses to the software can be avoided as much as possible. Accesses to the hardware are able only by the prevention of a direct access as the encircling are avoided in cupboards and shown EDP rooms with admission restriction and lockable cases.

The correspondence of the physical restriction of the access by a wall (of a case or building) corresponds the firewall (fire prevention wall) on software page. A firewall guards a Linux computer against attacks from the network. Linux computers without network access need no firewall.

Protection for your computer

Linux computers are sure from themselves relatively, because the design principle of computers of the Unix family was and is to connect only the inalienable and to permit.

Vandalism

Vandalism is directed against everything what is accessible to the attacker. The motivation of the attacker is often a play desire, curiosity or malicious pleasure in the farthest sense, unfortunately, also increasingly extortion. Behind resource abuse stand mostly economic interests or an ideology. With the resource abuse one or some features of a computer are used straight

Vandalism is directed against the effectiveness of a Linux computer. This can follow through damaging the software or through impediment of the network access.

For the damage of the software on the Linux computer the attacker must infiltrate either workable code on the Linux computer (Malicous code) or themselves a direct access on the Linux computer get (Hack). The infiltration of code often follows under exploitation of frequent, typical program mistakes of server programmes like the web servers or the ftp servers. An attacker can also get an unjustified access, while he guesses passwords or steals or program mistake in one of the programmes for the remote access like telnetd or sshd uses. Stealing is made easy for him particularly by programmes like telnet or ftp, because here the passwords uncoded over the network are transmitted and simple listening in (Sniffing) on the network betrays everything.

The impediment of the network access can follow through Denial-of-Service-Attacken. Besides, are set down - by himself legitimate - requirements for the Linux computer with so high frequency that no more capacity is available for the real assignments.

Resource abuse

Also a Linux computer can be used for unlawful actions. For the protection from pursuit it is tried to abuse the resources of computers of other owners for the unlawful purposes. This can be releasing of Denial-of-Service-Attacken against third as well as the saving of unlawful contents like pornography or pirated software and films and the mailing of spam mail. Spam mail is the mailing of e-mails of advertising content which are undesirable from the consignee. Spam has turned out as one of the biggest dangers for the effectiveness of the Internet.

Preventive measures

The first, easiest and most sure measure exists in switching off all of the services on a Linux computer which are not needed presently. If they are never needed, uninstalling should be also considered.

If a service is not required in full performance extent, the amount of the performances can be adapted generally about his configuration file. Still another with the clearly low performance extent which is enough for the claims is often available beside the installed service. This is valid in particular for web and ftp server.

Compilers are to be checked for her indispensability. They can be used to the production by Malicous code and should be removed - if not needed from the Linux computer.

Program mistakes in the server services and in the Kernel are supervised by special institutions (CERT = computer Emergency responses team). Their bulletins contain the mistake description and the remedy. The operating authority of a Linux computer directly linked with the Internet must read these bulletins regularly and obey the payments.

If offering of services is inalienable by a Linux computer on the Internet, the services must be protected after a careful installation and administration of the services against abuse with a firewall.

what is fstab?This is the main configuration file which retains all the information about the partitions and storage devices of your Linux system, which also shows how you can initialize and integrate them. Thus this is the main file, used while mounting so as to determine the options usable.Where is it located?fstab is located under /etc directory and so the exact path of the file is /etc/fstab.Basic StructureAs all of the Linux systems have bit different fstab file because of the different partitions and devices, still the basic structure is same. This has basically six columns:* First and Second: These tell about the device or partition and mount point (the point where data is to be attached to the file system) to the mount command. If you doesn't do the process manually, this file tells the defaults values. * Third: This column is here to tell about the file system type of the device or partition. * Fourth: This column lists the mount options and if the file system sho uld be mounted at boot or not. The others may include auto / noauto, dev / nodev, ro, rw and so on. * Fifth and Sixth: This one tells about dump and fsck options. The dump option uses a number to decide upon the backup of file system, whether it should be done or not. Fsck option tells about the order in which the file system should be checked. Corruption Problems and CureThe non-booting and non-mounting problems may be seen if this file becomes corrupt anyways. This can be a hard issue as you won't be able to use and run the system. Also, if you find that you can't access Windows partition from Linux, can't use floppy, CD etc. as usual, something is fishy with this file. The corruption in this file can be usual as this is a plain text file and this is very easy to open and edit, using any of the text editor, so the user faults can also make it corrupt, if he/she has the root privileges.Boot the system from the installation CD and try to correct the file, if you can't then r einstall the operating system. But at this last resort, do care of the data which you either have in your primary volume or whole of the hard drive (in case no disk partitioning is there). If you lose your important data in this case, try using Linux recovery programs as these are the only help which can benefit you Linux recovery after formatting.Data recovery Linux tools are instructed to perform a scan of the hard drive and recover all the lost data. Packaged with the interactive interface, the Linux recovery applications are the sure to get data after any case of loss.Stellar Phoenix Linux Data Recovery software is the most advanced and high-ending product for Linux data recovery. This data recovery Linux utility runs for Ext2, Ext3 and Reiser FS file systems and for all the flavors of Linux. The software uses the most powerful scanning procedure fo Linux recovery.

Linux file systems such as Ext2, Ext3 and Reiser FS file systems do the same organizing stuff for the files and directories, which the other file systems are expected to do. But, if one day you find symptoms like cross linked files, lost clusters or the invalid files and directories, these give you a strong hit of file system corruption. Though, usually the disk may appear performing well, but the file system scan may give you the unwilling results.If the extent of this problem is large then the culprit can be pointed towards file system corruption as otherwise small problems are common. The file system corruption is the serious issue to handle as ultimately the journey ends at requiring Linux recovery. However, you can try out the mentioned options, some of which are preventive tools: Viruses are the most threatening things for the Linux file systems, so make sure that you have an updated anti-virus program. Some recently installed software might be creating the problem . Uninstall it. Always make it a good habit that you turn off the system properly as this is the prime cause of Linux file system corruption. The instability of the operating system installation might be the issue, check for it. The recently installed bus mastering IDE drivers can also be an issue. Try uninstalling them. But if none of them may succeed in giving the effective results, have a fresh copy of Linux file system. But the solution may not sooth your data as that will not be located by the operating system due to the absence of pointers. Thus, all your data will be lost.Linux data recovery comes as the cure to track out all the lost data. In the file system corruption, there is no clue of the data, but the data recovery Linux software work out the effective scanning algorithms to work anyway. But remember that only the best Linux recovery application has the feature to work in severe file system corruption like case.Stellar Phoenix Linux Data Recovery is the appl ication to have the most valuable and expected Linux data recovery. The application goes good with Ext2, Ext3 and Reiser FS file systems and all the flavors of Linux operating system. This data recovery Linux program will scan the drive by the most powerful scanning algorithms, giving you an abstract view of the process.

After an unexpected shutdown, when you try to start your Linux computer, your system may refuse to boot and you might experience some error messages. The error message may sound like the followings:Your system appears to have shut down uncleanlyPress Y within 4 seconds to force file system integrity checkAs suggested in the error message, when you press Y, you may receive another error message stating:Checking root filesystem [/sbin/fsck.ext2 (1) -- /] fsck.ext2 - a / WARNING: couldn't open /etc/fstat: no such file or directoryext2fs_check_if_mount/The superblock could not read or does not describe a correct ext2 filesystem. If the device is valid and it really contains an ext2 filesystem (and not swap or ufs or something else), then the superblock is corrupt, and you might try running e2fsck with an alternate superblock: e2fsck -b 8193 :No such file or directory while determining whether / is mounted.fsck.ext2: Is a directory while trying to open //etc/rc.d/rc.sysinit: li ne 415: failure: command not found.After these errors, the system does not boot and you can not access your valuable data from hard drive and thus may face the nightmare of data loss. CauseThis behavior of Linux operating system occurs due to severely corrupted root file system. Due to the same, operating system can not find the required files to boot and thus shows you the error messages. In Linux operating system, the root file system is the file system which is used to manage data on the root partition, the partition is the one on which operating system is installed. Root file system contains very important file and corruption to this will put you in need of Linux Recovery.Linux Data Recovery is the process of retrieving missing, lost or inaccessible data from Linux hard drive. It is best possible using Linux Recovery Software. These software are able to scan your hard drive, locate the lost data and then carry out Linux Recovery. Stellar Phoenix Linux Data Recovery sof tware is the best ever made and the most comprehensive Linux Recovery Software. It is powerful enough to thoroughly scan your hard drive and retrieve all of your data from it. Phoenix Linux Data Recovery is compatible with most of the Linux flavors.

CRC (Cyclic Redundancy Check) is the standard check process that different files use to detect corruption inconsistencies, if any. Using this check, Linux systems ensure that kernel image hasn't changed after it was built. If system finds any mismatch between the original and current value, it doesn't proceed further while booting and eventually the system halts. Data becomes inaccessible and to restore lost information, you need to use your recent data backup. But if it gives errors or is found as incomplete or damaged, Linux Data Recovery applications can be used for data recovery. You might encounter the following error message when trying to boot your Linux-based computer:"CRC error - System Halted"This error message occurs immediately after system prompts: 'Uncompressing Linux'. System doesn't boot up and you cannot use CTRL-ALT-DEL key to reset the system.CausePossible causes of the above issue to occur are:* Kernel image is stored on bad sectors. When Linux kernel i mage gets uncompressed, it runs a CRC check to ensure its integrity. If checksum values don't match, it gives errors, as above. * Bad hard drive* Bad hardware components like system memory or CPU cache* File system issuesSolutionYou should follow these methods in order to fix this problem:* Use Live CD to boot your system. After this, you need to copy the kernel image from the bootable disk and delete the existing kernel image. Rename the copied image to the one that boot loader recognizes. If you use LILO (LInux LOader), you should run /sbin/lilo to translate present location of copied image to disk geometry language and write to partition's boot sector.* Backup all the possible data and replace the bad hard drive* Diagnose and replace the damaged hardware components* Run fsck, if file system is dirty* If problem persists, reformat the hard drive and restore from backupDisk formatting deletes all the existing information and if you observe any issues with your backup, you c an use Linux Recovery tools. These are effective Linux Data Recovery software that restore lost information using powerful and safe scanning algorithms. Stellar Phoenix Linux Data Recovery is an optimum tool to locate and recover lost data. It supports Ext2, Ext3, and ReiserFS file systems. This Linux Recovery tool provides advanced features including Disk Imaging, RAW File Recovery, File Filer etc. The application is compatible with most of the Linux distributions, like Red Hat, SlackWare, Turbo Linux, Sorcerer, SUSE etc.