mikemaccana's questions

Is there a way for an SMTP server to tell an MTA that a user has moved to a new address?

There are many SMTP return codes, including for common situations like Mailboxes being full, the address not existing, the message being rejected etc.

Is there currently, or is there a proposal, to allow a server to respond to incoming mail with an error code that the user has changed email addresses and is now available at a new domain?

Again, draft proposals are OK. I've looked in RFC 5321 section 4.2.3 and perhaps '251: user not local will forward' works but I'm not sure how email practically works in 2020.

Use case: users migrating between email providers is a common scenario and I can imagine having a grace period (where the old provider lets incoming MTAs know the user has moved to another address) has probably been discussed before.

Example a user was [email protected], but has have moved to bar.com. foo.com is happy to let incoming connections know that this identity is now at a different domain, and that senders should update their address books, for some period of time (say 12 months), before foo.com no longer provides any service for this identity at all.

I have downloaded the official BIND 9 Windows binaries from ISC. They don't do anything:

$ .\host.exe google.com
$ (no output)

Same with dig. How do I make host, dig etc work on Windows?

I have a current generation Linux system I'd like to use with haproxy. Journald will happily log stdout from .service, and mark the log as coming from that service, but haproxy doesn't seem to be able to log to stdout.

What's the simplest and cleanest way to get haproxy to log to systemd/journald?

Edit: current configuration is the default:

global
    log         127.0.0.1 local2

But there's no local2 facility since there's no syslog on the local box.

I've been using iptables for a long time, but have never used firewalld until recently. I have enabled port 3000 TCP via firewalld with the following command:

# firewall-cmd --zone=public --add-port=3000/tcp --permanent

However I can't access the server on port 3000. From an external box:

telnet 178.62.16.244 3000
Trying 178.62.16.244...
telnet: connect to address 178.62.16.244: Connection refused

There are no routing issues: I have a separate rule for a port forward from port 80 to port 8000 which works fine externally. My app is definitely listening on the port too:

Proto Recv-Q Send-Q Local Address           Foreign Address         State       User       Inode      PID/Program name
tcp        0      0 0.0.0.0:3000            0.0.0.0:*               LISTEN      99         36797      18662/node

firewall-cmd doesn't seem to show the port either - see how ports is empty. You can see the forward rule I mentioned earlier.

# firewall-cmd --list-all
public (default, active)
  interfaces: eth0
  sources:
  services: dhcpv6-client ssh
  ports:
  masquerade: no
  forward-ports: port=80:proto=tcp:toport=8000:toaddr=
  icmp-blocks:
  rich rules:

However I can see the rule in the XML config file:

# cat /etc/firewalld/zones/public.xml
<?xml version="1.0" encoding="utf-8"?>
<zone>
  <short>Public</short>
  <description>For use in public areas. You do not trust the other computers on networks to not harm your computer. Only selected incoming connections are accepted.</description>
  <service name="dhcpv6-client"/>
  <service name="ssh"/>
  <port protocol="tcp" port="3000"/>
  <forward-port to-port="8000" protocol="tcp" port="80"/>
</zone>

What else do I need to do to allow access to my app on port 3000?

Also: is adding access via a port the correct thing to do? Or should I make a firewalld 'service' for my app instead?

I am using a key pair called 'newkey' on many instances. I wish to keep using this key, but change the name of the key pair (obviously 'newkey' is quite vague, and won't be new forever).

Please note: there are a lot of similar questions, like https://stackoverflow.com/questions/7881469/change-key-pair-for-ec2-instance, about changing the keypair on a running instance. This is a different topic.

Is there's an option to start a container immediately on creation? Looking through the Create a Container docs I can't see one, but I suspect something like this may already exist.

In older Linux systems, the logger command can be used to send a log message to syslog.

Reading where does logger log its messages to in Arch Linux?, it seems that syslog messages and the logger command line app only talk to the systemd journal if a socket for message forwarding is set up.

So what's the modern equivalent of the logger command? How can I send a message directly to the systemd journal from the command line?

I'm following the CoreOS Docker Documentation and it mentions starting containers with commands like:

docker run someImageName /bin/somebinary

Where someImageName is an image. When /bin/somebinary exits, the image will no longer be running.

I would simply like to run an image, without specifying any binaries to run. Instead, I simply want to run the services (eg, systemd / sysvinit) that are normally run inside the images OS.

This seems like the most common thing anyone would ever want to do with Docker, but trying to run an image without a command returns:

2014/02/05 14:49:19 Error: create: No command specified

How can I start a Docker container and run a full OS, rather than specifying a command?

I've been testing a minimal Fedora install. To check the path for interpreters like python or node, I normally use which.

I notice which isn't installed by default. I could add the package, but I wonder if there's a shell builtin that can be used to perform this common task.

I'm using bash 4.2.

I have a number of distinct etcd clusters, I would like to be centrally controlled:

• I have multiple distinct etcd clusters. Hosts in one cluster should not have any access to config in another cluster.

• The central hosts should be able to read and write to all clusters, as this hosts role is to see and control all the clusters.

I'm not quite sure how to implement this.

• Can a single host running etcd be a member of multiple clusters?
• Does etcd allow me to to have a host that can communicate with multiple clusters?

I'd like to run a series of commands inside part of a script, and stop if any return a non-zero exit status. But also, inside the same script, I'd like a final command to always run, regardless of whether anything failed before.

#!/usr/bin/env bash
set -e
(
  # various commands go here
) &> /var/log/logfile
final_command_that_always_runs /var/log/logfile

Is this possible?

Perhaps I can 'set -e' for only one () section of a script?

Core dump limits are disabled for a user using the normal /etc/security/limits.conf mechanism:

# ulimit -a  
core file size        (blocks, -c) unlimited

However, running a segfault test shows no core being dumped:

/tmp/a.out  
Segmentation fault

No 'core dumped' message. Hrm. /etc/security/limits.conf looks as follows:

username            -        core            unlimited

Has anyone encountered this before? Is this a bug in SLES? Thanks.