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 MyApp->config->{session} = {
                storage => '/tmp/session'
        };

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Specifies the directory root to be used for the sharing of session data. The default value will use File::Spec to find the default tempdir, and use a file named MyApp/session/data, where MyApp is replaced with the appname.

Note that the file will be created with mode 0640, which means that it will only be writeable by processes running with the same uid as the process that creates the file. If this may be a problem, for example if you may try to debug the program as one user and run it as another, specify a directory like /tmp/session-$>, which includes the UID of the process in the filename.

directory_umask

The directories in the session on the filesystem should be globally writable to allow for multiple users. While this is a potential security concern, the actual cache entries are written with the user's umask, thus reducing the risk of cache poisoning. If you desire it to only be user writable, set the 'directory_umask' option to '077' or similar. Defaults to '000' unless explicitly set.
SEE ALSO

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At server startup, before child processes are spawned, [...]

Be careful with the startup file. Everything run at server initialization is run with root privileges if you start the server as root (which you have to do unless you choose to run the server on an unprivileged port, numbered 1024 or higher). [...]