This is one of those posts that helps me remember how to do something I knew how to do once but would inevitably forget how to do again one millisecond later. In this case it is how to configure a directory that is shared on the network but only to registered users.
First off, create a new group for the users (I will use the group name sharegroup as an example):
sudo addgroup sharegroup
Then add yourself to the group:
sudo usermod -aG sharegroup $USER
Add any other users to the group in the same way.
Now it is time to prepare the directory to be shared. Create (or choose) the directory and share it using the local network share option from the GUI. Alternatively, edit /etc/samba/smb.conf directly by adding something like this at the bottom:
path = <full path to shared directory>
writeable = yes
guest ok = no
read only = no
browsable = yes
create mask = 0770
directory mask = 0770
valid users = @sharegroup
and then restart samba:
sudo systemctl restart smbd
Then the directory group ownership must be set to the new group. Set the directory as current and enter:
sudo chgrp -R sharegroup *
sudo chgrp sharegroup .
Be very careful any time using the -R option with sudo as it is easy to completely mess up the OS! Generally it is best to start in the directory that’s being modified. That way, there’s less chance of making unintentional modifications.
Now change the permissions to allow group members to operate on files properly:
sudo chmod -R g+rw *
sudo chmod g+rw .
Then the users must be added to samba – for example:
sudo smbpasswd -a $USER
This will ask for a password to be used to access the share. That’s it!
I really like using JSON encoding as a way of transferring messages between processes as it is machine and language independent. Plus, it is very well suited to stream processing networks (such as rt-ai Edge) as arbitrary fields can be added to existing JSON messages and passed along. Contrast this with compiled IDLs which typically have no flexibility whatsoever.
One problem though is that binary data cannot be included in JSON messages directly. Typically base64 encoding is used to convert binary data into text. However, this is inefficient, especially in a stream processing network where base64 decoding and encoding might have to be done several times.
There are a variety of modifications to JSON around but it is very simple to just add binary data on to the end of a JSON message to form a complete message that can be transferred via MQTT for example.
In Python, an MQTT message can be published like this:
def publish(topic, jsonData, binData = None):
jsonDump = json.dumps(jsonData)
jsonString = struct.pack('>I', len(jsonDump)) + jsonDump + binData
Here, jsonData contains the normal JSON message text, binData contains the binary data to be sent along with it. To receive the message, use something like this:
def onMessage(client, userdata, message):
jsonLength = struct.unpack('>I', message.payload[0:4])
jsonData = json.loads(message.payload[4:4+jsonLength])
binData = message.payload[4+jsonLength:]
Easy but not particularly memorable, enter this to set output volume to 60% for example:
amixer set Master 60%
I think that pretty much every time I upgrade Ubuntu something breaks in the GStreamer area. Generally it is a case of plugins going missing. On this occasion, the H.264 decoder was missing. This can be installed with:
sudo apt-get install gstreamer1.0-libav
Hardly an original post but there are so many variants around that, when I need to do this and have (as usual) forgotten how to do it, I can’t find anything that works! So here is my variant…
Add an entry for wlan0 to the /etc/network/interfaces file:
iface wlan0 inet dhcp
Then, create /etc/wpa_supplicant.conf to use WPA encryption (this link has examples of other modes):
That’s it for DHCP. To use a static IP address, change the /etc/network/interfaces entry (with the appropriate customizations) to be:
iface wlan0 inet static
For no good reason at all my Mac Mail app started crashing on launch and would not stop. A quick Google search found this article – the key bits are reproduced here to make things easier.
Open Finder and select the Go menu option. While holding down Option, select the Library option (which is otherwise invisible). Navigate to Mail/V2/MailData. In that folder there will be a number of files starting with “Envelope Index”. Move (not copy) all of these out to the Desktop or somewhere safe just in case. Then, launch the Mail app. It will re-import the messages (which might take a long time depending on how many there are – about 20 minutes in my case) and then everything should be back to normal. If that worked, the original index files can be deleted.
It’s pretty annoying that, by default, USB serial devices come up with somewhat restricted permissions. Sometimes adding the user to the dialout group works, sometimes it doesn’t. The most reliable way to fix this for all time is to add a udev rule but I can never remember the syntax, hence this post…
Continue reading “Linux: setting permissions for USB serial ports using udev rules”