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<h2 class="title" style="clear: both"><a id="env_open"></a>berkdb env</h2>
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<pre class="programlisting">berkdb env
[-cachesize {gbytes bytes ncache}]
[-create]
[-data_dir dirname]
[-encryptaes passwd]
[-encryptany passwd]
[-errfile filename]
[-home directory]
[-log_dir dirname]
[-mode mode]
[-private]
[-recover]
[-recover_fatal]
[-shm_key shmid]
[-system_mem]
[-tmp_dir dirname]
[-txn [nosync]]
[-txn_max max]
[-use_environ]
[-use_environ_root] </pre>
<p>
The <span class="bold"><strong>berkdb env</strong></span> command opens and
optionally creates a database environment. The returned environment
handle is bound to a Tcl command of the form <span class="bold"><strong>envN</strong></span>, where N is an integer starting at 0 (for
example, env0 and env1). It is through this Tcl command that the
script accesses the environment methods. The command automatically
initializes the Shared Memory Buffer Pool subsystem. This subsystem
is used whenever the application is using any Berkeley DB access
method.
</p>
<p>
The options are as follows:
</p>
<div class="itemizedlist">
<ul type="disc">
<li>
<p>
<span class="bold"><strong>-cachesize {gbytes bytes ncache}</strong></span>
</p>
<p>
Set the size of the database's shared memory buffer pool (that is, the
cache), to <span class="bold"><strong>gbytes</strong></span> gigabytes plus
<span class="bold"><strong>bytes</strong></span>. The cache should be the size
of the normal working data set of the application, with some small
amount of additional memory for unusual situations. (Note: The working
set is not the same as the number of simultaneously referenced pages,
and should be quite a bit larger!)
</p>
<p>
The default cache size is 256KB, and may not be specified as less than
20KB. Any cache size less than 500MB is automatically increased by
25% to account for buffer pool overhead; cache sizes larger than 500MB
are used as specified.
</p>
<p>
It is possible to specify caches to Berkeley DB that are large enough
so that they cannot be allocated contiguously on some architectures;
for example, some releases of Solaris limit the amount of memory that
may be allocated contiguously by a process. If <span class="bold"><strong>ncache</strong></span> is 0 or 1, the cache will be allocated
contiguously in memory. If it is greater than 1, the cache will be
broken up into <span class="bold"><strong>ncache</strong></span> equally sized
separate pieces of memory.
</p>
<p>
For information on tuning the Berkeley DB cache size, see
<a href="../../programmer_reference/general_am_conf.html#am_conf_cachesize" class="olink">Selecting a Cache Size</a>
in the <em class="citetitle">Berkeley DB Programmer's Reference Guide</em>.
</p>
</li>
<li>
<p>
<span class="bold"><strong>-create</strong></span>
</p>
<p>
Cause Berkeley DB subsystems to create any underlying files, as
necessary.
</p>
</li>
<li>
<p>
<span class="bold"><strong>-data_dir dirname</strong></span>
</p>
<p>
Specify the environment's data directory as described in
<a href="../../programmer_reference/env_naming.html" class="olink">Berkeley DB File Naming</a>
in the <em class="citetitle">Berkeley DB Programmer's Reference Guide</em>.
</p>
</li>
<li>
<p>
<span class="bold"><strong>-encryptaes passwd</strong></span>
</p>
<p>
Specify the database should be encrypted with the given password using
the Rijndael/AES (also known as the Advanced Encryption Standard and
Federal Information Processing Standard (FIPS) 197) algorithm.
</p>
</li>
<li>
<p>
<span class="bold"><strong>-encryptany passwd</strong></span>
</p>
<p>
Specify the already existing environment should be opened with the
given password. This option is used if the environment is known to be
encrypted, but the specific algorithm used is not known.
</p>
</li>
<li>
<p>
<span class="bold"><strong>-errfile filename</strong></span>
</p>
<p>
When an error occurs in the Berkeley DB library, a Berkeley DB error
or an error return value is returned by the function. In some cases,
however, the errno value may be insufficient to completely describe
the cause of the error especially during initial application
debugging.
</p>
<p>
The <span class="bold"><strong>-errfile</strong></span> argument is used to
enhance the mechanism for reporting error messages to the application
by specifying a file to be used for displaying additional Berkeley DB
error messages. In some cases, when an error occurs, Berkeley DB will
output an additional error message to the specified file reference.
</p>
<p>
consist of the environment command name (for example, env0) and a
colon (":"), an error string, and a trailing <newline>
character.
</p>
<p>
This error-logging enhancement does not slow performance or
significantly increase application size, and may be run during normal
operation as well as during application debugging.
</p>
</li>
<li>
<p>
<span class="bold"><strong>-home directory</strong></span>
</p>
<p>
The <span class="bold"><strong>-home</strong></span> argument is described in
<a href="../../programmer_reference/env_naming.html" class="olink">Berkeley DB File Naming</a>
in the <em class="citetitle">Berkeley DB Programmer's Reference Guide</em>.
</p>
</li>
<li>
<p>
<span class="bold"><strong>-log_dir dirname</strong></span>
</p>
<p>
Specify the environment's logging file directory as described in
<a href="../../programmer_reference/env_naming.html" class="olink">Berkeley DB File Naming</a>
in the <em class="citetitle">Berkeley DB Programmer's Reference Guide</em>.
</p>
</li>
<li>
<p>
<span class="bold"><strong>-mode mode</strong></span>
</p>
<p>
On UNIX systems, or in IEEE/ANSI Std 1003.1 (POSIX) environments, all
files created by Berkeley DB are created with mode <span class="bold"><strong>mode</strong></span> (as described in <span class="bold"><strong>chmod</strong></span>(2)) and modified by the process' umask
value at the time of creation (see <span class="bold"><strong>umask</strong></span>(2)). The group ownership of created
files is based on the system and directory defaults, and is not
further specified by Berkeley DB. If <span class="bold"><strong>mode</strong></span> is 0, files are created readable and
writable by both owner and group. On Windows systems, the mode
argument is ignored.
</p>
</li>
<li>
<p>
<span class="bold"><strong>-private</strong></span>
</p>
<p>
Specify that the environment will only be accessed by a single process
(although that process may be multithreaded). This flag has two
effects on the Berkeley DB environment. First, all underlying data
structures are allocated from per-process memory instead of from
shared memory that is potentially accessible to more than a single
process. Second, mutexes are only configured to work between threads.
</p>
<p>
This flag should not be specified if more than a single process is
accessing the environment, as it is likely to cause database
corruption and unpredictable behavior. For example, if both a server
application and the Berkeley DB utility
<a href="../C/db_stat.html" class="olink">db_stat</a>
will access the environment, the <span class="bold"><strong>-private</strong></span> option
should not be specified.
</p>
</li>
<li>
<p>
<span class="bold"><strong>-recover</strong></span>
</p>
<p>
Run normal recovery on this environment before opening it for normal
use. If this flag is set, the <span class="bold"><strong>-create</strong></span>
option must also be set because the regions will be removed and
re-created.
</p>
</li>
<li>
<p>
<span class="bold"><strong>-recover_fatal</strong></span>
</p>
<p>
Run catastrophic recovery on this environment before opening it for
normal use. If this flag is set, the <span class="bold"><strong>-create</strong></span> option must also be set since the
regions will be removed and re-created.
</p>
</li>
<li>
<p>
<span class="bold"><strong>-shm_key key</strong></span>
</p>
<p>
Specify a base segment ID for Berkeley DB environment shared memory
regions created in system memory on systems supporting X/Open-style
shared memory interfaces, for example, UNIX systems supporting
shmget(2) and related System V IPC interfaces. See
<a href="../../programmer_reference/env_region.html" class="olink">Shared Memory Regions</a>
in the <em class="citetitle">Berkeley DB Programmer's Reference Guide</em> for more information.
</p>
</li>
<li>
<p>
<span class="bold"><strong>-system_mem</strong></span>
</p>
<p>
Allocate memory from system shared memory instead of memory backed by
the filesystem. See
<a href="../../programmer_reference/env_region.html" class="olink">Shared Memory Regions</a>
in the <em class="citetitle">Berkeley DB Programmer's Reference Guide</em> for more information.
</p>
</li>
<li>
<p>
<span class="bold"><strong>-tmp_dir dirname</strong></span>
</p>
<p>
Specify the environment's tmp directory, as described in
<a href="../../programmer_reference/env_naming.html" class="olink">Berkeley DB File Naming</a>
in the <em class="citetitle">Berkeley DB Programmer's Reference Guide</em>.
</p>
</li>
<li>
<p>
<span class="bold"><strong>-txn [nosync]</strong></span>
</p>
<p>
Initialize the Transaction subsystem. This subsystem is used when
recovery and atomicity of multiple operations and recovery are
important. The <span class="bold"><strong>-txn</strong></span> option implies
the initialization of the logging and locking subsystems as well.
</p>
<p>
If the optional <span class="bold"><strong>nosync</strong></span> argument is
specified, the log will not be synchronously flushed on transaction
commit. This means that transactions exhibit the ACI (atomicity,
consistency, and isolation) properties, but not D (durability); that
is, database integrity will be maintained, but it is possible that
some number of the most recently committed transactions may be undone
during recovery instead of being redone.
</p>
<p>
The number of transactions that are potentially at risk is governed by
how often the log is checkpointed (see
<a href="../C/db_checkpoint.html" class="olink">db_checkpoint</a>
in the <em class="citetitle">Berkeley DB C API</em> guide for more information) and how many
log updates can fit on a single log page.
</p>
</li>
<li>
<p>
<span class="bold"><strong>-txn_max max</strong></span>
</p>
<p>
Set the maximum number of simultaneous transactions that are supported
by the environment, which bounds the size of backing files. When
there are more than the specified number of concurrent transactions,
calls to <span class="emphasis"><em>env</em></span> <span class="bold"><strong>txn</strong></span>
will fail (until some active transactions complete).
</p>
</li>
<li>
<p>
<span class="bold"><strong>-use_environ</strong></span>
</p>
<p>
The Berkeley DB process' environment may be permitted to specify
information to be used when naming files; see
<a href="../../programmer_reference/env_naming.html" class="olink">Berkeley DB File Naming</a>
in the <em class="citetitle">Berkeley DB Programmer's Reference Guide</em>. Because
permitting users to specify which files are used can create security
problems, environment information will be used in file naming for all
users only if the <span class="bold"><strong>-use_environ</strong></span> flag
is set.
</p>
</li>
<li>
<p>
<span class="bold"><strong>-use_environ_root</strong></span>
</p>
<p>
The Berkeley DB process' environment may be permitted to specify
information to be used when naming files; see
<a href="../../programmer_reference/env_naming.html" class="olink">Berkeley DB File Naming</a>
in the <em class="citetitle">Berkeley DB Programmer's Reference Guide</em>. As
permitting users to specify which files are used can create security
problems, if the <span class="bold"><strong>-use_environ_root</strong></span>
flag is set, environment information will be used for file naming only
for users with appropriate permissions (for example, users with a
user-ID of 0 on IEEE/ANSI Std 1003.1 (POSIX) systems).
</p>
</li>
</ul>
</div>
<p>
The <span class="bold"><strong>berkdb env</strong></span> command returns an
environment handle on success.
</p>
<p>
In the case of error, a Tcl error is thrown.
</p>
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