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Workaround and fixes for the current Core Dump Handling vulnerability affected kernels

Workaround and fixes for the current Core Dump Handling vulnerability affected kernels






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April, 26th. 2006:

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Section: GDBM User Reference (1)
Updated: July 12, 2016
Index Return to Main Contents


gdbmtool - examine and modify a GDBM database  


gdbmtool [-lmNnqrs] [-b SIZE] [-c SIZE]
 [-f FILE] [--block-size=SIZE]
         [--cache-size=SIZE] [--file FILE]  [--newdb] [--no-lock]
         [--no-mmap] [--norc]
         [--quiet] [--read-only] [--synchronize] [DBFILE]

gdbmtool [-Vh] ][--help] [--usage] [--version]  


The gdbmtool utility allows you to view and modify an existing GDBM database or to create a new one.

The DBFILE argument supplies the name of the database to open. If not supplied, the default name junk.gdbm is used instead. If the named database does not exist, it will be created. An existing database can be cleared (i.e. all records removed from it) using the --newdb option (see below).

Unless the -N (--norc) option is given, after startup gdbmtool looks for file named .gdbmtoolrc first in the current working directory, and, if not found there, in the home directory of the user who started the program. If found, this file is read and interpreted as a list of gdbmtool commands.

Then gdbmtool starts a loop, in which it reads commands from the standard input, executes them and prints the results on the standard output. If the standard input is attached to a console, the program runs in interactive mode.

The program terminates when the quit command is given, or end-of-file is detected on its standard input.

A gdbmtool command consists of a command verb, optionally followed by one or more arguments, separated by any amount of white space. A command verb can be entered either in full or in an abbreviated form, as long as that abbreviation does not match any other verb.

Any sequence of non-whitespace characters appearing after the command verb forms an argument. If the argument contains whitespace or unprintable characters it must be enclosed in double quotes. Within double quotes the usual escape sequences are understood, as shown in the table below:

        Escape      Expansion
        \a          Audible bell character (ASCII 7)
        \b          Backspace character (ASCII 8)
        \f          Form-feed character (ASCII 12)
        \n          Newline character (ASCII 10)
        \r          Carriage return character (ASCII 13)
        \t          Horizontal tabulation character (ASCII 9)
        \v          Vertical tabulation character (ASCII 11)
        \\          Single slash

In addition, a backslash immediately followed by the end-of-line
character effectively removes that character, allowing to split long arguments over several input lines.  


-b, --block-size=SIZE
Set block size.
-c, --cache-size=SIZE
Set cache size.
-f, --file=FILE
Read commands from FILE, instead of from the standard input.
-l, --no-lock
Disable file locking.
-m, --no-mmap
Do not use mmap(2).
-n, --newdb
Create the database, truncating it if it already exists.
-q, --quiet
Don't print initial banner.
-r, --read-only
Open database in read-only mode.
-s, --synchronize
Synchronize to disk after each write.
-h, --help
Print a short usage summary.
Print a list of available options.
-V, --version
Print program version


Print the avail list.
bucket NUM
Print the bucket number NUM and set is as the current one.
Print the bucket cache.
Close the currently open database.
Print the number of entries in the database.
Print the current bucket.
delete KEY
Delete record with the given KEY.
Print hash directory.
export FILE-NAME [truncate] [binary|ascii]
Export the database to the flat file FILE-NAME. This is equivalent to gdbm_dump(1).

This command will not overwrite an existing file, unless the truncate parameter is also given. Another optional parameter determines the type of the dump (*note Flat files::). By default, ASCII dump will be created.

fetch KEY
Fetch and display the record with the given KEY.
Fetch and display the first record in the database. Subsequent records can be fetched using the next command (see below).
hash KEY
Compute and display the hash value for the given KEY.
Print file header.
help or ?
Print a concise command summary, showing each command letter and verb with its parameters and a short description of what it does. Optional arguments are enclosed in square brackets.
Shows the command history list with line numbers. This command is available only if the program was compiled with GNU Readline.
history COUNT.
Shows COUNT latest commands from the command history.
history N COUNT.
Shows COUNT commands from the command history starting with Nth command.
import FILE-NAME [replace] [nometa]
Import data from a flat dump file FILE-NAME. If the replace argument is given, any records with the same keys as the already existing ones will replace them. The nometa argument turns off restoring meta-information from the dump file.
List the contents of the database.
next [KEY]
Sequential access: fetch and display the next record. If the KEY is given, the record following the one with this key will be fetched.
open FILE
Open the database file FILE. If successful, any previously open database is closed. Otherwise, if the operation fails, the currently opened database remains unchanged.

This command takes additional information from the variables open, lock, mmap, and sync. See the section VARIABLES, for a detailed description of these.

Close the database and quit the utility.
Reorganize the database.
set [VAR=VALUE...]
Without arguments, lists variables and their values. If arguments are specified, sets variables. Boolean variables can be set by specifying variable name, optionally prefixed with no, to set it to false.
source FILE
Read commands from the given FILE.
Print current program status.
store KEY DATA
Store the DATA with the given KEY in the database. If the KEY already exists, its data will be replaced.
unset VARIABLE...
Unsets listed variables.
Print the version of gdbm.


The define statement provides a mechanism for defining key or content structures. It is similar to the C struct declaration:

define key|content { defnlist }

The defnlist is a comma-separated list of member declarations. Within defnlist the newline character looses its special meaning as the command terminator, so each declaration can appear on a separate line and arbitrary number of comments can be inserted to document the definition.

Each declaration has one of the following formats

type name
type name [N]

where type is a data type and name is the member name. The second format defines the member name as an array of N elements of type.

The supported types are:

        type        meaning
        char        single byte (signed)
        short       signed short integer
        ushort      unsigned short integer
        int         signed integer
        unsigned    unsigned integer
        uint        ditto
        long        signed long integer
        ulong       unsigned long integer
        llong       signed long long integer
        ullong      unsigned long long integer
        float       a floating point number
        double      double-precision floating point number
        string      array of characters (see the NOTE below)
        stringz     null-terminated string of characters

The following alignment declarations can be used within defnlist:

offset N
The next member begins at offset N.
pad N
Add N bytes of padding to the previous member.

For example:

define content {
        int status,
        pad 8,
        char id[3],
        stringz name

To define data consisting of a single data member, the following simplified construct can be used:

define key|content type

where type is one of the types discussed above.

NOTE: The string type can reasonably be used only if it is the last or the only member of the data structure. That's because it provides no information about the number of elements in the array, so it is interpreted to contain all bytes up to the end of the datum.  


confirm, boolean
Whether to ask for confirmation before certain destructive operations, such as truncating the existing database. Default is true.
ps1, string
Primary prompt string. Its value can contain conversion specifiers, consisting of the % character followed by another character. These specifiers are expanded in the resulting prompt as follows:

        Sequence    Expansion
        %f          name of the db file
        %p          program name
        %P          package name (gdbm)
        %_          horizontal space (ASCII 32)
        %v          program version
        %%          %

The default prompt is %p>%_.

ps2, string
Secondary prompt. See ps1 for a description of its value. This prompt is displayed before reading the second and subsequent lines of a multi-line command.

The default value is %_>%_.

delim1, string
A string used to delimit fields of a structured datum on output (see the section DATA DEFINITIONS).

Default is , (a comma). This variable cannot be unset.

delim2, string
A string used to delimit array items when printing a structured datum.

Default is , (a comma). This variable cannot be unset.

pager, string
The name and command line of the pager program to pipe output to. This program is used in interactive mode when the estimated number of output lines is greater then the number of lines on your screen.

The default value is inherited from the environment variable PAGER. Unsetting this variable disables paging.

quiet, boolean
Whether to display welcome banner at startup. This variable should be set in a startup script file.

The following variables control how the database is opened:

cachesize, numeric
Sets the cache size. By default this variable is not set.
blocksize, numeric
Sets the block size. Unset by default.
open, string
Open mode. The following values are allowed:
Truncate the database if it exists or create a new one. Open it in read-write mode.
wrcreat or rw
Open the database in read-write mode. Create it if it does not exist. This is the default.
reader or readonly
Open the database in read-only mode. Signal an error if it does not exist.
lock, boolean
Lock the database. This is the default.
mmap, boolean
Use memory mapping. This is the default.



gdbm_dump(1), gdbm_load(1), gdbm(3).  


Report bugs to <>.  


Copyright © 2013 Free Software Foundation, Inc
License GPLv3+: GNU GPL version 3 or later <>
This is free software: you are free to change and redistribute it. There is NO WARRANTY, to the extent permitted by law.




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