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annotate docs/nitros9guide/dcheck.refentry @ 1404:097d8033bccc
source improvements
| author | boisy |
|---|---|
| date | Thu, 27 Nov 2003 23:46:01 +0000 |
| parents | 4dae346c4969 |
| children | b00cf13c9f61 |
| rev | line source |
|---|---|
| 135 | 1 <refentry id="dcheck"> |
| 2 <refnamediv> | |
| 3 <refname>DCHECK</refname> | |
| 4 <refpurpose>Check Disk File Structure</refpurpose> | |
| 5 </refnamediv> | |
| 6 | |
| 7 <refsynopsisdiv> | |
| 8 <cmdsynopsis> | |
| 1093 | 9 <command>dcheck</command> |
| 135 | 10 <arg choice="opt"> |
| 11 <option>-opts</option> | |
| 12 </arg> | |
| 13 <arg choice="plain"> | |
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14 <replaceable>devnam</replaceable> |
| 135 | 15 </arg> |
| 16 </cmdsynopsis> | |
| 17 </refsynopsisdiv> | |
| 18 | |
| 19 <refsect1><title>Description</title> | |
| 20 <para> | |
| 21 It is possible for sectors on a disk to be marked as being allocated | |
| 22 but in fact are not actually associated with a file or the disk's | |
| 23 free space. This can happen if a disk is removed from a drive while | |
| 24 files are still open, or if a directory which still contains files | |
| 1093 | 25 is deleted (see <xref linkend="sec3.5"/>). <command>Dcheck</command> is a diagnostic that can be used to |
| 135 | 26 detect this condition, as well as the general integrity of the directory/file linkages. |
| 27 </para> | |
| 28 <para> | |
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29 <command>Dcheck</command> is given as a parameter the name of the disk device to be |
| 135 | 30 checked. After verifying and printing some vital file structure |
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31 parameters, <command>dcheck</command> follows pointers down the disk's file system tree |
| 135 | 32 to all directories and files on the disk. As it does so, it |
| 33 verifies the integrity of the file descriptor sectors, reports any | |
| 34 discrepancies in the directory/file linkages, and builds a sector | |
| 35 allocation map from the segment list associated with each file. If | |
| 36 any file descriptor sectors (FDs) describe a segment with a cluster | |
| 37 not within the file structure of the disk, a message is reported | |
| 38 like: | |
| 39 </para> | |
| 40 <screen> | |
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41 *** Bad FD segment ($xxxxxx-$yyyyyy) for file: <replaceable>pathlist</replaceable> |
| 135 | 42 </screen> |
| 43 <para> | |
| 44 This indicates that a segment starting at sector xxxxxx and ending | |
| 45 at sector yyyyyy cannot really be on this disk. Because there is a | |
| 46 good chance the entire FD is bad if any of it's segment descriptors | |
| 47 are bad, the allocation map is <emphasis>not</emphasis> updated for corrupt FDs. | |
| 48 </para> | |
| 49 <para> | |
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50 While building the allocation map, <command>dcheck</command> also makes sure that each |
| 135 | 51 disk cluster appears only once and only once in the file structure. |
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52 If this condition is detected, <command>dcheck</command> will display a message like: |
| 135 | 53 </para> |
| 54 <screen> | |
| 55 Cluster $xxxxxx was previously allocated | |
| 56 </screen> | |
| 57 <para> | |
| 58 This message indicates that cluster xxxxxx has been found at least | |
| 59 once before in the file structure. The message may be printed more | |
| 60 than once if a cluster appears in a segment in more than one file. | |
| 61 </para> | |
| 62 <para> | |
| 63 The newly created allocation map is then compared to the allocation | |
| 64 map stored on the disk, and any differences are reported in messages | |
| 65 like: | |
| 66 </para> | |
| 67 <screen> | |
| 68 Cluster $xxxxxx in allocation map but not in file structure | |
| 69 Cluster $xxxxxx in file structure but not in allocation map | |
| 70 </screen> | |
| 71 <para> | |
| 72 The first message indicates sector number xxxxxx (hexadecimal) was | |
| 73 found not to be part of the file system, but was marked as allocated | |
| 74 in the disk's allocation map. In addition to the causes mentioned | |
| 75 in the first paragraph, some sectors may have been excluded from the | |
| 76 allocation map by the FORMAT program because they were defective or | |
| 77 they may be the last few sectors of the disk, the sum of which was | |
| 78 two small to comprise a cluster. | |
| 79 </para> | |
| 80 <para> | |
| 81 The second message indicates that the cluster starting at sector | |
| 82 xxxxxx is part of the file structure but is <emphasis>not</emphasis> | |
| 83 marked as allocated | |
| 84 in the disk's allocation map. It is possible that this cluster may | |
| 85 be allocated to another file later, overwriting the contents of the | |
| 86 cluster with data from the newly allocated file. Any clusters that | |
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87 have been reported as "previously allocated" by <command>dcheck</command> as described |
| 135 | 88 above surely have this problem. |
| 89 </para> | |
| 90 <para> | |
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91 Available <command>dcheck</command> options are: |
| 135 | 92 </para> |
| 93 | |
| 94 <informaltable frame="none"> | |
| 95 <tgroup cols="2"> | |
| 648 | 96 <colspec colwidth="1.3in"/> |
| 97 <colspec colwidth="3in"/> | |
| 135 | 98 <tbody> |
| 99 <row> | |
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100 <entry>-w=<replaceable>path</replaceable></entry> |
| 135 | 101 <entry>pathlist to directory for work files</entry> |
| 102 </row> | |
| 103 <row> | |
| 104 <entry>-p</entry> | |
| 105 <entry>print pathlists for questionable clusters</entry> | |
| 106 </row> | |
| 107 <row> | |
| 108 <entry>-m</entry> | |
| 109 <entry>save allocation map work files</entry> | |
| 110 </row> | |
| 111 <row> | |
| 112 <entry>-b</entry> | |
| 113 <entry>suppress listing of unused clusters</entry> | |
| 114 </row> | |
| 115 <row> | |
| 116 <entry>-s</entry> | |
| 117 <entry>display count of files and directories only</entry> | |
| 118 </row> | |
| 119 <row> | |
| 120 <entry>-o</entry> | |
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121 <entry>print <command>dcheck</command>'s valid options</entry> |
| 135 | 122 </row> |
| 123 </tbody> | |
| 124 </tgroup> | |
| 125 </informaltable> | |
| 126 | |
| 127 <para> | |
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128 The "-s" option causes <command>dcheck</command> to display a count of files and |
| 135 | 129 directories only; only FDs are checked for validity. The "-b" option |
| 130 suppresses listing of clusters allocated but not in file structure. | |
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131 The "-p" option causes <command>dcheck</command> to make a second pass through the file |
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132 structure printing the pathlists for any clusters that <command>dcheck</command> finds |
| 135 | 133 as "already allocated" or "in file structure but not in allocation |
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134 map". The "-w=" option tells <command>dcheck</command> where to locate it's allocation |
| 135 | 135 map work file(s). The pathlist specified must be a FULL pathlist to |
| 136 a <emphasis>directory</emphasis>. The directory "/D0" is | |
| 137 used is used if "-w" is not | |
| 138 specified. It is recommended that this pathlist NOT be located on | |
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139 the disk being <command>dcheck</command>ed if the disk's file structure integrity is in |
| 135 | 140 doubt. |
| 141 </para> | |
| 142 <para> | |
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143 <command>Dcheck</command> builds its disk allocation map in a file called |
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144 <replaceable>pathlist</replaceable>/DCHECKppO, where <replaceable>pathlist</replaceable> |
| 135 | 145 is as specified by the |
| 146 "-w=" option and pp is the process number in hexadecimal. Each bit | |
| 147 in this bitmap file corresponds to a cluster of sectors on the disk. | |
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148 If the "-p" option appears on the command line, <command>dcheck</command> creates a |
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149 second bitmap file (<replaceable>pathlist</replaceable>/DCHECKpp1) that has a bit set for |
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150 each cluster <command>dcheck</command> finds as "previously allocated" or "in file |
| 135 | 151 structure but not in allocation map" while building the allocation |
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152 map. <command>Dcheck</command> them makes another pass through the directory structure |
| 135 | 153 to determine the pathlists for these questionable clusters. These |
| 154 bitmap work files may be saved by specifying the "-m" option on the | |
| 155 command line. | |
| 156 </para> | |
| 157 </refsect1> | |
| 158 <refsect1><title>Restrictions</title> | |
| 159 <para> | |
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160 For best results, <command>dcheck</command> should have exclusive access to the disk |
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161 being checked. Otherwise <command>dcheck</command> may be fooled if the disk allocation map |
| 135 | 162 changes while it is building its bitmap file from the |
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163 changing file structure. <command>Dcheck</command> cannot process disks with a directory |
| 135 | 164 depth greater than 39 levels. |
| 165 </para> | |
| 166 <para> | |
| 1093 | 167 For more information see: <xref linkend="sec3.10"/>, |
| 168 <xref linkend="sec3.5"/>, | |
| 169 <command>format</command>, | |
| 170 6.1 of OS-9 Systems Programmer's Manual | |
| 135 | 171 </para> |
| 172 </refsect1> | |
| 173 <refsect1><title>Examples</title> | |
| 174 <screen> | |
| 175 OS9: dcheck /d2 (workfile is on /D0) | |
| 176 | |
| 177 Volume - 'My system disk' on device /d2 | |
| 178 $009A bytes in allocation map | |
| 179 1 sector per cluster | |
| 180 $0004D0 total sectors on media | |
| 181 Sector $000002 is start of root directory FD | |
| 182 $0010 sectors used for id, allocation map and root directory | |
| 183 Building allocation map work file... | |
| 184 Checking allocation map file... | |
| 185 | |
| 186 | |
| 187 'My system disk' file structure is intact | |
| 188 1 directory | |
| 189 2 files | |
| 190 | |
| 191 OS9: dcheck -mpw=/d2 /d0 | |
| 192 Volume - 'System disk' on device /d0 | |
| 193 $0046 bytes in allocation map | |
| 194 1 sector per cluster | |
| 195 $00022A total sectors on media | |
| 196 Sector $000002 is start of root directory FD | |
| 197 $0010 sectors used for id, allocation map and root directory | |
| 198 Building allocation map work file... | |
| 199 Cluster $00040 was previously allocated | |
| 200 *** Bad FD segment ($111111-$23A6F0) for file: /d0/test/junky.file | |
| 201 Checking allocation map file... | |
| 202 Cluster $000038 in file structure but not in allocation map | |
| 203 Cluster $00003B in file structure but not in allocation map | |
| 204 Cluster $0001B9 in allocation map but not in file structure | |
| 205 Cluster $0001BB in allocation map but not in file structure | |
| 206 | |
| 207 Pathlists for questionable clusters: | |
| 208 Cluster $000038 in path: /d0/OS9boot | |
| 209 Cluster $00003B in path: /d0/OS9boot | |
| 210 Cluster $000040 in path: /d0/OS9boot | |
| 211 Cluster $000040 in path: /d0/test/double.file | |
| 212 | |
| 213 1 previously allocated clusters found | |
| 214 2 clusters in file structure but not in allocation map | |
| 215 2 clusters in allocation map but not in file structure | |
| 216 1 bad file descriptor sector | |
| 217 | |
| 218 'System disk' file structure is not intact | |
| 219 5 directories | |
| 220 25 files | |
| 221 </screen> | |
| 222 </refsect1> | |
| 223 </refentry> | |
| 224 |