I have a question with respect to Mongo DB Master / Slave setup on to the same machine .
I am using Ubutu 12 as OS .
Do i need to have two copies of MongoDB in the same machine ??
If yes , how can it allow to install two times seperately ??
(sudo apt-get install mongodb-10gen)
Since all the linked questions are for Windows and this is a Linux command I will divert from the "Possible duplicate" comment.
Yes you can run multiple mongods on the same machine. Instead of installing multiple times you just start mongod differently like such:
./mongod --dbpath /foo/bar/otherpath --port some_other_port
source: https://serverfault.com/questions/296246/multiple-mongos-on-one-server
But it is not recommended to do this due to resource contention, especially for memory. It will be horrid for even a development server and if you intend to put this setup into production then you might as well just go for one mongod.
If you want to run multiple instances on the same machine it is instead recommended to use containers such as virtual machines or something else. There are a few out there.
Related
I am attempting to debug some C# / .NET 5 code in WSL 2 with Ubuntu on Windows. I have WSL 2 setup with Windows 10 and want to test out creating a Systemd service. Unfortunately, it appears Systemd is not enabled with WSL 2 by default, even though a standard Ubuntu install does have it enabled by default. Is there any way to get Systemd enabled in WSL 2?
Note: See footnote at bottom of this answer for background on this Community Wiki.
There are several possible paths to enabling Systemd on WSL2 (but not WSL1). These are summarized here, with more detail provided below.
Option 1: Upgrade WSL to the latest application release (if supported by your system) and opt-in to the Systemd feature
Option 2: Run a Systemd-helper script designed for WSL2
Option 3: Manually run Systemd in its own namespace
And while not part of this question, for those simply looking to run certain applications that require Systemd, there are alternatives:
On WSL1 and WSL2:
Alternative 1: SysVInit scripts (e.g. sudo service <service_name> start) where available
Alternative 2: Manually configuring and running the service
On WSL2-only:
Alternative 3: Docker
Should you enable Systemd in WSL?
First, consider whether you should or need to enable Systemd in WSL. Enabling Systemd will automatically start a number of background services and tasks that you really may not need under WSL. As a result, it will also increase WSL startup times, although the impact will be dependent on your system. Check the Alternatives section below to see if there may be a better option that fits your needs. For example, the service command may do what you need without any additional effort.
More detail on each answer:
Option 1: Upgrade WSL to the latest application release (if supported by your system) and opt-in to the Systemd feature
Microsoft has now integrated Systemd support in the WSL2 application release (as opposed to the older "Windows feature" implementation).
Starting with WSL Application Release 1.0.0, this feature is available on both Windows 10 and Windows 11. Windows 10 users do need to be on UBR (update build revision) 2311 or later. The UBR is the last 4 digits of your full Windows build number (e.g. 10.0.19045.2311 for Windows 10 22H2). 2311 is installed with KB5020030, an optional Preview update, although if you are reading this later, it will likely be a later (non-Preview) monthly servicing update.
If you are on a supported Windows release, the WSL application with Systemd support can be installed:
Through the Microsoft Store (as "Windows Subsystem for Linux").
Or from the Releases page in the Github repo. To install a release manually:
Reboot (to make sure that WSL is not in use at all). A simple wsl --shutdown may work, but often will not.
Download the 1.0.0 (or later) release from the link above.
Start an Administrator PowerShell and:
Add-AppxPackage <path.to>/Microsoft.WSL_1.0.0.0_x64_ARM64.msixbundle
wsl --version # to confirm
To enable, start your Ubuntu (or other Systemd) distribution under WSL (typically just wsl ~ will work).
sudo -e /etc/wsl.conf
Add the following:
[boot]
systemd=true
Exit Ubuntu and again:
wsl --shutdown
Then restart Ubuntu.
sudo systemctl status
... should show your Systemd services.
Option 2: Run a Systemd-helper script designed for WSL2
There are a number of Systemd-enablement scripts available from various sources. Given the complexities involved in running Systemd under WSL, it is recommended that you:
Use one that is actively maintained
Attempt to understand, as much as possible, how they operate, and how they may impact other features and applications in your distribution(s) under WSL
When asking questions here or on any other site, disclose in the question which script you are using so that others can attempt to understand and/or reproduce your issue in the proper context
Several of the more popular projects that enable Systemd under WSL2 are:
Genie: 1.8k stars, last commit September, 2022
Distrod: 1.4k stars, last commit July 2022
WSL2-Hacks: 1.1k stars, mostly instructional, with a supporting script example. Last commit January, 2022
At the core, all of them operate on the same principles covered in the next option ...
Option 3: Manually run Systemd in its own namespace
One of the main issues with running Systemd in earlier versions of WSL is that both inits need to be PID 1. To get around this, it is possible to create a new namespace or container where Systemd can run as PID 1.
To see how this is done (at a very basic level):
Run:
sudo -b unshare --pid --fork --mount-proc /lib/systemd/systemd --system-unit=basic.target
This starts Systemd in a new namespace with its own PID mapping. Inside that namespace, Systemd will be PID1 (as it must, to function) and own all other processes. However, the "real" PID mapping still exists outside that namespace.
Note that this is a "bare minimum" command-line for starting Systemd. It will not have support for, at least:
Windows Interop (the ability to run Windows .exe)
The Windows PATH (which isn't necessary without Windows Interop anyway)
WSLg
The scripts and projects listed above do extra work to get these things working as well.
Wait a few seconds for Systemd to start up, then:
sudo -E nsenter --all -t $(pgrep -xo systemd) runuser -P -l $USER -c "exec $SHELL"
This enters the namespace, and you can now use ps -efH to see that systemd is running as PID 1 in that namespace.
At this point, you should be able to run systemctl.
And after proving to yourself that it's possible, it is recommended that you exit all WSL instances completely, then doing wsl --shutdown. Otherwise, some things will be "broken" until you do. They can likely be "fixed", but that's beyond the scope this answer. If you are interested, please refer to the projects listed above to see how they handle these situations.
Alternative 1: SysVInit scripts (e.g. sudo service <service_name> start) where available
In Ubuntu, Debian, and some other distributions on WSL, many of the common system services still have the "old" init.d scripts available to be used in place of systemctl with Systemd units. You can see these by using ls /etc/init.d/.
So, for example, you can start ssh with sudo service ssh start, and it will run the /etc/init.d/ssh script with the start argument.
Even some non-default packages such as MySql/MariaDB will install both the Systemd unit files and the old init.d scripts, so you can still use the service command for them as well.
On the hand, some packages, like Elasticsearch, only install Systemd units. And some distributions only provide Systemd units for most (if not all) packages in their repositories.
Alternative 2: Manually configuring and running the service
For those services that don't have a init-script equivalent, it can be possible to run them "manually".
For simplicity, let's assume that the ssh init.d script wasn't available.
In this case, the "answer" is to figure out what the Systemd unit files are doing and attempt to replicate that manually. This can vary widely in complexity. But I'd start with looking at the Systemd unit file that you are trying to run:
less /lib/systemd/system/ssh.service
# Trimmed
[Service]
EnvironmentFile=-/etc/default/ssh
ExecStartPre=/usr/sbin/sshd -t
ExecStart=/usr/sbin/sshd -D $SSHD_OPTS
RuntimeDirectory=sshd
RuntimeDirectoryMode=0755
Some of the less relevant lines have been trimmed to make it easier to parse, but you can man systemd.exec, man systemd.service, and others to see what most of the options do.
In this case, when you sudo systemctl start ssh, it:
Reads environment variables (the $SSHD_OPTS) from /etc/default/ssh
Tests the config, exits if there is a failure
Makes sure the RuntimeDirectory exists with the specified permissions. This translates to /run/sshd (from man systemd.exec). This also removes the runtime directory when you stop the service.
Runs /usr/sbin/sshd with options
So, if you don't have any environment-based config, you could just set up a script to:
Make sure the runtime directory exists. Note that, since it is in /run, which is a tmpfs mount, it will be deleted after every restart of the WSL instance.
Set the permissions to 0755
Start /usr/sbin/sshd as root
... And you would have done the same thing manually without Systemd.
Again, this is probably the simplest example. You might have much more to work through for more complex tasks.
Alternative 3: Docker
Many packages/services are available as Docker images. Docker typically runs very well under Ubuntu on WSL2 (specifically WSL2; it will not run on WSL1). If there's not a SysVinit "service" script for the service you are trying to start, there may very well be a Docker image available that runs in a containerized environment.
Example: Elasticsearch, as in this question.
Bonus #1: Doesn't interfere with other packages already installed (no dependency issues).
Bonus #2: The Docker images themselves pretty much never use Systemd, so you can often inspect the Dockerfile to see how the service is started without Systemd. For more information see the next option - "The manual way."
Microsoft recommends Docker Desktop for Windows for running Docker containers under WSL2.
Footnote This answer is being posted as a Community Wiki because it can apply to multiple Stack Overflow questions. It is originally based on answers to this Ask Ubuntu question. However, it is hoped that this wiki-answer can be continuously updated by the community as Systemd evolves on WSL.
This question has been chosen since:
It appears to be the most canonical, straightforward, "How do I enable Systemd on WSL?" question.
It is on-topic, as *creating Systemd services is (or at least can-be) unique to programming.
I am learning docker and during my project, i can't enter the mongo db with this command:
mongo -u "username" -p "mypassword"
It throws me this error:
bash: mongo: command not found
I am not sure what the issue is. I have installed the community edition of mongo db and i also tried different terminals but i can't enter the db.
Any suggestions?
Thanks in advance!
I assume, you did the following: Create docker-compose.yml as you wrote before. Start docker compose up. This will start a container on your system, having mongodb installed in it. It will not affect your "normal" system outside this container. (You can imagine it as kind of a virtual machine, though it is not really the same.) So, if you did not install mongodb on your local host system as well, the error you encounter is quite explicable.
If you want to access the mongodb running within the container, you have two possibilities:
1. From outside the container (which is the more common use case)
You will have to install mongo on your regular PC (or anywhere you want to access your db from) as well. Then you would issue mongo 127.0.0.1:3000. The 3000 is important as your docker-compose.yml says, mongo is listening on port 3000. Note that you might have to get your network configuration adapted before this works, especially from other PCs, where 127.0.0.1 won't be correct.
2. From within the container
Once your container is started, you can also execute a command inside it, like this: docker exec -it ${container_id} /bin/bash. You'll have to find out the container's ID beforehand, using something like docker-compose ps -q. This will start a bash shell inside the container and "connect" you to it. (If there's no /bin/bash installed in the container, this will not work. Try e. g. /bin/sh instead.) Now your terminal will be inside the container and just be able to use the commands present there. So, to get back to your local PC, don't forget to issue exit.
Conclusion
IMHO, the crucial point is, that the physical PC you are working in front of and the container running inside it are almost completely different systems, connected only by the docker daemon and some virtual network access. You'll have to keep that in mind and decide what you want to do/run inside the container and what to do outside, on the host.
Here is a little further reference that might help you. And this answer is about how to find out your container ID in an automated way. (Assuming that you are running just that one container!)
I am working with 2 projects using 2 different versions of mongodb. One is using 3.2.10 and the other using 2.6. My current system has the latest version, and this is incompatible with the old project.
Is there a way to install & use both version of Mongo?
Yes. You can download two archives and extract them into two different bin directories. You will need to register each instance as a separate service to allow them to be ran in the background. Also configure each one to listen on different port. Obviously each project will need to be configured with correct port.
By default mongod listens on port 27017. You can use any other ports that are not used by other applications. Here is the example of how you can start two mongo services manually. Ports below are chosen arbitrarily.
~/installFolder1/mongod --dbpath /pathToDatabase/database1 --port 27010
~/installFolder2/mongod --dbpath /pathToDatabase/database2 --port 27011
I am using Ubuntu 14.04 LTS and I have installed MongoDB 3.2.1. I had various problems with it that I fixed by either finding help from the internet (thanks Google) or by uninstalling and re-installing MongoDb.
One persistent problem that I cannot fix, unless I re-install, is by running mongod on the terminal. Currently my mongodb installation is working properly. With sudo service mongod start I start mongodb (I commented out start on xxxx line at /etc/init/mongod.conf so it doesn't auto start.) and with sudo service mongod stop I can stop it normally atm. And it correctly uses /var/lib/mongodb path for saving my collections.
If however after I stop mongodb with sudo service mongod stop I hit, on the terminal, mongod then mongodb breaks. I have gotten all kinds of errors like
Unusable mongod.lock. I have gotten around it, in a previous install, by doing sudo mongod but that was not a proper solution.
/data/db folder not found !!. Why look for it in the first place? The /etc/mongod.conf specifies the dbpath /var/lib/mongodb which is also the default when mongodb gets installed !!?? I have gotten around it as well with the mongod --dbpath /var/lib/mongodb option.
I think there was one more error that I don't remember but I also fixed/gotten_around it by finding solutions online.
I know that by re-installing and by never running mongod I can - for now? - not face those problems again (which looks a much better solution that the "workarounds" I did whenever those problems arose. I am wondering however what it is that is going wrong when I type mongod instead of sudo service mongod start ?!
In case somebody tries to replicate the problem know that I ve done only two modifications on my system after installing:
Commenting out the start on xxxx line at /etc/init/mongod.conf
Disabling transparent hugepages as described on the answer here.
I don't think anyone of those should interfere with my installation.
Can anyone help me understand what is going on? Aren't those commands supposed to do the same thing??
Thanks for your help.
Ok, I will try to answer.
First, unless you know what you are doing, you should not start mongod manually.
In general (a bit simplified), calling [sudo] service mongod start, you instruct the system to read the according file in /etc/init and start the executable according to the configuration described in said file.
When you started mongod by hand, however, you actually called the mongod binary, the server software itself – while the name is the same as the service, the two commands have few things in common. The binary does not use the /etc/mongod.conf by default, falling back to its default values for the various settings. Actually, you can see that the config file is explicitly defined in the init script. This is why mongod tried to find /data/db.
You can find said binary by issuing
which mongod
Regarding the lock file: When mongod is started by the system, user root actually assumes the effective user id of mongod (or mongodb I don't know for Ubuntu of the top of my head). When you tried to start it from your user id, you do not have the privileges to overwrite the lock file. When you used sudo mongod afterwards, you assumed the effective user id of root which on the other hand is allowed to overwrite said file. However, mongod will the run as root which is a security no-no.
An init script defines which environment to use, which user to run under and a lot of other stuff. Unless you really know what you are doing, you should not even fiddle with them, much less skip it.
And now, with the finger up
sudo is not the UNIX way of saying "I mean it!"
It has security implications, and you should be very aware of those implications before using it – aka read the man pages of every command you issue before you use it until you have at least a fact based idea of what the command is doing.
And again: unless you really know (as opposed to assume) what you are doing, do not fiddle with the system configuration.
There is a datastorage, an mysql container, a php and a nginx. Is it possible to let these processes run on different oses?
So one is on debian, the other on centos and so on?
Example
this one is debian
docker run --name sql -d buildsql
this one is centos
docker run --name php --linked sql:db -d buildphp
Containers talk to each other over the network, so they are normally unaware of the OS being used by other containers, in exactly the same way that your browser doesn't really care about the OS of the webservers it talks to.
Most of the official images are based on Debian, so you quite often find your containers are all running Debian, but there's no need for this to be true. Some containers don't have an OS at all and just contain a binary that gets run when the container starts.
In short, there is no problem in using different OSs, unless you have some funky application specific problem with networking.