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COMPUTER BITS BY JENNIFER BONNITCHA More things to do when things go wrong This month we have more troubleshooting tips particularly ways of repairing damaged files. Should you encounter problems with unexpected program termination, one of the first things you should do is check for file damage. When you need to find out if there is any file damage, the DOS command CHKDSK (CHecK DiSK) is a good starting point. Its job is to check the formatted size and available space on a disc, indicate the amount of disc space consumed by system files, data files and bad sectors, and finally show the standard memory size and amount of memory available. As a safety measure, it's a good idea to run CHKDSK occasionally on all your regularly used hard and floppy discs to prevent minor problems from turning into major ones. This is an external DOS command, so you need to make sure a copy of the file is available either in the current directory or its location CHKDSK has two switches you can use in conjunction with the command: /f (FIX) instructs CHKDSK to attempt to correct any errors detected. CHKDSK always asks if it should attempt to correct errors it detects, however it will actually do nothing unless this switch is specified /v (VERBOSE) this switch directs CHKDSK to display filename and path specifications for each file on the disc. Using the DOS pipe (I) and FIND commands, you can find a file on a hard disc: CHKDSK C:/V I FIND FILENAME You should initially run CHKDSK without the /f switch to determine what type of error may have taken "Should you receive an Abort, Retry, Fail, Ignore command while running CHKDSK, avoid the Ignore option. If you do choose Ignore, the corrective action taken by CHKDSK could cause further problems." must be included in the Path command. CHKDSK analyses the entire disc and in doing so, compares each subdirectory entry size against the File Allocation Table (FAT), checks the integrity of each allocation chain in the FAT and can optionally repair some forms of file damage. 50 SILICON CHIP place. You should also note that CHKDSK is not designed for use with the DOS commands JOIN, SUBST or ASSIGN since it only reports on real rather than logical drives. For this reason, CHKDSK should not be run on a network disc drive either. The command CHKDSK [drive] will typically return something like that shown in Fig.1. The disc is examined and if all is OK, no errors are reported. The status report displays information about the disc and the computer's memory. The first four lines report on the total amount of disc space, the number of files on the disc and the remaining available space. You may see a bad sector report as well. The remaining two lines report . on the amount of conventional memory used and the amount still available. You can re-direct the output from CHKDSK to either a file or printer if you wish using the command: CHKDSK [drive]> [FILENAME] or CHKDSK [drive] > PRN In addition, if you include a filename in the command, CHKDSK will display the number of non-contiguous areas (or sectors) on the disc that contain the name files. Although fragmented files (ie, those with non-con- · tiguous blocks) are acceptable to DOS, they can slow down your computer's performance quite considerably. If you use the DOS wildcard . * , CHKDSK reports on each fragmented file in the current directory. Should you receive an Abort, Retry, Fail, Ignore command while running CHKDSK, avoid the Ignore option. If you do choose Ignore, the corrective action taken by CHKDSK could be incorrect and only cause further problems. Try the Retry option several times if needed and then for preference use the Fail or Abort option. Ignore•is the absolute last resort. · Problems you may have CHKDSK can get confused over two problems and thus will abort the procedure itself: Cannot CHDIR to <file specifier> CHDIR .. failed trying alternate method Failures are usually caused by car- When the file is closed, DOS writes ing the chase eventually become the new information to the FAT and if memory-resident interrupted, the FAT chain is incomplete, the file's directory entry is inin the DOS disc Volume LABELNAME created Dec 12, 1991 3:15p consistent and the data may or may buffers, so the drive 71442432 bytes total disk space light will go out not actually exist on the disc. A physi110592 bytes in 3 hidden files cally or logically damaged directory until you restart the 225280 bytes in 34 directories computer. Listen may also create this problem. 57335808 bytes in 960 user files also for a rhythmic Provided you used the If switch 13770752 bytes available on disk pattern to the disc when running CHKDSK, you can reply "Y" to the convert message. DOS will movement. 655360 bytes total memory then create a separate file for each Detecting the 320704 bytes free lost chain. These files are named problem file is FILExxxx.CHK (where xxxx represents easier if you redirect the CHKDSK a sequential number starting with rupt interrupt tables or insufficient output to a printer (CHKDSK > PRN). 0000). Should you decide to answer RAM. In the first instance, the file tree You will most likely receive another "N", DOS converts to zero the entries cannot be processed beyond the point error message, then CHKDSK will fail in the FAT that correspond to the lost specified. When directories are cre- again. Once this happens, halt the chains and marks those areas as availated, DOS automatically inserts two program, restart DOS then use the Iv able for new files. entries. The first entry in each switch so CHKDSK can display the If you have not used the If switch, subdirectory is the "." entry (dot) name of each file it checks. The last CHKDSK reports the amount of disc which represents the directory itself. file shown is usually the suspect file. space that could be freed, regardless The second entry is the given name When (if) you find the problem file(s), of your answer to the conversion ques" .. " (double dot) which represents the you can either delete the file and hope tion. Answering "Y" will cause parent of the current directory. If ei- all the associated chains are also deCHKDSK to report the number of files ther of these entries is corrupted, leted. You could use a program like that would be created. CHKDSK displays the first message. Norton's FASTSAVE or Mace Utilities You could, depending on the value CHKDSK will ask if you want to SAVE-RESTORE to repair the FAT or of the lost chains, answer "Y" to the convert the directory to a file. Answering yes creates a standard file containing the contents of the subdirectory (ie, the file names). The ac"A cluster is lost if the FAT entry for the cluster is tual contents of the files become lost a non zero number but the cluster does not clusters when the subdirectory is conbelong to any file. A contiguous set of lost verted. However, you get the chance to do something about the lost clusclusters is a lost chain." ters at the conclusion of the CHKDSK command, provided you used the If switch. finally, format the disc to re-generate conversion question then examine the You could get this message during the FAT (but, of course, destroy all file's contents. CHKDSK if you have a temporary hardexisting information). Cross linking ware glitch in the disc controller or Little orphan Annies interface. FILENAME is cross-linked: If CHKDSK locks up, it has entered a xxx lost clusters found in yyy chains On cluster xx loop in which one link in the file''s Convert lost chains to files (YIN)? Two files are cross-linked when the chain in the FAT points back to an A cluster is a unit of space on a FAT indicates that a cluster belongs to earlier link. During processing, should disc. A cluster is "lost" if the FAT both files. The message is displayed a wayward entry point to a previous entry for the cluster is a non zero once for each file that is cross-linked. FAT entry for the file, CHKDSK enters number but the cluster does not be- CHKDSK doesn't take any action and an endless loop moving backward and long to any file. A contiguous set of the files can often be salvaged by copyforward to trace the chain. The trace lost clusters is a lost chain. ing them to another physical disc or continues forever and can be broken The most probable cause of this partition. You should then delete the using the <CTRL BREAK> or <CTRL ALT problem is that a program or DOS Gross-linked files and examine the DEL> key sequence (or, if you have stopped before DOS finished closing copies. !f the files are intact, run one on your computer, press the Rethe file. This error occurs only when CHKDSK again for the suspect disc set). extending a previous file or when cre- and if all is OK, copy the files back to You can be reasonably certain you ating new files. CHKDSK has found the original disc. Remember that once are in a loop when CHKDSK displays some clusters without an owner. When you delete the files, they are almost no message, there is no disc activity a file is created or extended, DOS impossible to recover. for approximately 30 seconds, or the marks the clusters it will write to as We'll have more adventures next drive keeps working beyond an acin-use, thus creating the link in the month on checking and repairing disc ceptable limit. The FAT sections causfile's FAT chain. damage. SC FIGURE 1 FEBRUARY1992 51