snapshot.py - DirectoryStorage Snapshot Tool
snapshot.py [options] COMMAND COMMAND A command to be run when in snapshot mode.
--storage DIRECTORY Indicate the DirectoryStorage home directory. The --storage switch may only be omitted if you are the old (pre 1.1.10) command line syntax. -v Make it more verbose. -q Make it less verbose. -t SECONDS If something else has locked snapshot mode, keep retrying for the specified number of seconds. (default: no retries) -s SECONDS Sleep for the specified number of seconds between retries. (default: 10 seconds) --snapshot-conf FILE Override the default path to the snapshot.conf configuration file. The default is DIRECTORY/config/snapshot.conf
This tool will force the storage into snapshot mode using the methods described in the config/snapshot.conf file. Snapshot mode guarantees that the storage directory contains only whole ZODB transactions, and that the main storage files will not be modified. Any live storage process retains full read/write access.
Once in snapshot mode it will lock the relevent files in the storage directory to ensure that it remains a coherent snapshot while the COMMAND is run. COMMAND is only run once shapshot mode is guaranteed.
As of version 1.1.10, this tool is not needed for running single instances of the checkds.py tool (to check the storage for corruption) or the backup tool. However snapshot.py is still useful when scripting these other tools. It is the only way to access the retry mechanism. It allows you to run a script which, for example, checks the storage before taking a backup inside one single snapshot.
If it successfully enters snapshot mode, snapshot.py will exit with the same exit code as COMMAND. It will have a non-zero exit code if COMMAND was not run.
This file is stored in the config directory of the storage. It contains lines which describe methods which the tool can try to force the storage into snapshot mode. Each line must be of the form:
- Use direct file access to put the storage into snapshot mode. This will only work if nothing else is using the storage. Versions since 1.1.11 will attempt to use this method even if not listed in the file, or if the file is missing. Use 'nodirect' to inhibit this.
- http URL ACCESS
- Use xmlrpc into Zope to put the storage into snapshot mode, and take it back out again once COMMAND has finished. This will only work if Zope (possibly via ZEO) is using the storage. URL is of a DirectoryStorageToolkit instance in the Zope server. ACCESS is the name of a file which contains username and password of a Zope user authorized to use that DirectoryStorageToolkit, on one line seperated by a colon. Note that this format is compatible with zope's 'access' file, although snapshot.py supports only cleartext passwords. In version 1.1.9 and earlier, a relative filename in this field will be considered to be relative to the current working directory. In version 1.1.10 and later, it is relative to the directory containing snapshot.conf.
Note that it can be useful to list more that one url, for example if the same storage can be accessed through more than one Zope server.
This error is shown if it is unable to lock the storage directory into snapshot mode. This indicates that:
- It could not communicate with the Zope server to switch it into snapshot mode. DirectoryStorageToolkit configuration? Bad URLs? Overzealous firewall? Maybe you forgot to patch ZEO, as described in doc/INSTALL.txt.
- It is configured to use the wrong Zope server. Using the -v switch will include a Entered snapshot using.... message.
- Your zope server crashed, and therefore was unable to perform a normal clean shutdown which leaves the storage directory in a snapshot state. (or you have used the quick_shutdown option in the storage configuration file, which inhibits this tidy shutdown process). Also you included the nodirect option preventing the snapshot tool from forcing it into snapshot mode directly (or you are using a version before 1.1.11 which does not try direct access automatically).
- Some other process is using direct access into the storage directory which prevents this tool using direct access.
Note that there is no problem if your Zope servers shutdown cleanly. It leaves the storage in a snapshot state, and the snapshot.py tool can lock it in that state. For this reason the snapshot tool will not show any warnings even if all of the Zope servers listed in snapshot.conf are inaccessible.
Version 1.1.9 and before supported a different command line format of the form:
snapshot.py DIRECTORY PATH-TO-SNAPSHOT-CONF COMMAND
It was possible to specify "-" as the path to snapshot.conf, which indicated that the default location should be used. This command line format is still supported today, although the format listed above is preferred.