04-27-2010
Good Practice Guides
A recent post where someone suggested redirecting with a clobber ">" to a file the same command was reading from prompted me to post this sysad good practice list. Some items are from times where I have learned things the hard way. I think this would be helpful so we can learn from each others mistakes.
1. Test thy backups
2. pwd before rm
3. hostname before reboot
4. Executing a command with a recursive option on .* can be unpredictable
5. One word. Clustering
6. Test patches on a staging machine
7. If you are going to do it frequently, script it
8. Don't redirect to a file you are reading from
9. Copy a file before editing it
10. Document your systems' configuration and topology
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LEARN ABOUT DEBIAN
dbus-uuidgen
dbus-uuidgen(1) General Commands Manual dbus-uuidgen(1)
NAME
dbus-uuidgen - Utility to generate UUIDs
SYNOPSIS
dbus-uuidgen [--version] [--ensure[=FILENAME]] [--get[=FILENAME]]
DESCRIPTION
The dbus-uuidgen command generates or reads a universally unique ID.
Note that the D-Bus UUID has no relationship to RFC 4122 and does not generate UUIDs compatible with that spec. Many systems have a sepa-
rate command for that (often called "uuidgen").
See http://www.freedesktop.org/software/dbus/ for more information about D-Bus.
The primary usage of dbus-uuidgen is to run in the post-install script of a D-Bus package like this:
dbus-uuidgen --ensure
This will ensure that /var/lib/dbus/machine-id exists and has the uuid in it. It won't overwrite an existing uuid, since this id should
remain fixed for a single machine until the next reboot at least.
The important properties of the machine UUID are that 1) it remains unchanged until the next reboot and 2) it is different for any two run-
ning instances of the OS kernel. That is, if two processes see the same UUID, they should also see the same shared memory, UNIX domain
sockets, local X displays, localhost.localdomain resolution, process IDs, and so forth.
If you run dbus-uuidgen with no options it just prints a new uuid made up out of thin air.
If you run it with --get, it prints the machine UUID by default, or the UUID in the specified file if you specify a file.
If you try to change an existing machine-id on a running system, it will probably result in bad things happening. Don't try to change this
file. Also, don't make it the same on two different systems; it needs to be different anytime there are two different kernels running.
The UUID should be different on two different virtual machines, because there are two different kernels.
OPTIONS
The following options are supported:
--get[=FILENAME]
If a filename is not given, defaults to localstatedir/lib/dbus/machine-id (localstatedir is usually /var). If this file exists and
is valid, the uuid in the file is printed on stdout. Otherwise, the command exits with a nonzero status.
--ensure[=FILENAME]
If a filename is not given, defaults to localstatedir/lib/dbus/machine-id (localstatedir is usually /var). If this file exists then
it will be validated, and a failure code returned if it contains the wrong thing. If the file does not exist, it will be created
with a new uuid in it. On success, prints no output.
--version
Print the version of dbus-uuidgen
AUTHOR
See http://www.freedesktop.org/software/dbus/doc/AUTHORS
BUGS
Please send bug reports to the D-Bus mailing list or bug tracker, see http://www.freedesktop.org/software/dbus/
dbus-uuidgen(1)