Technical FAQ
Why can't I "talk" to my instances?
Here are a few common reasons for broken connectivity to your instance.
An instance's state is changed to running as soon as we start to boot your OS. This means there
will be some delay (possibly a few minutes depending on your configuration) during which your
instance will not have been fully set-up. After this period, it should be fully functional.
Additionally, you will need to make sure you have authorized the appropriate access to your host
through the Amazon EC2 firewall. If you have launched your instances without specifying a
security group, the default group is used. Permissions on the default group are very strict by
default and disallow all access from the Internet and other groups. You will need to add
permissions to your default group or you will have to set up a new group with appropriate
permissions. See the developer guide for more information on the “Securing the Network”.
Assuming you have authorized port 22, a useful debugging tool is to try to open an ssh connection
with verbose output. You should use the man page to get the exact syntax for your system, but the
command is likely to look like ssh -vv root@[hostname]. This output would be very useful if
posting to the forum.
Why did my instance terminate immediately after launch?
Launch errors may be the result of an internal error during launch or a corrupt Amazon EC2
image. The former should be rare, and we actively test for and isolate suspect hosts. You should
use the “DescribeInstances” API to look for more details on why your instance failed to launch.
NB: the ec2-describe-instances command line tool does not conveniently print out this
information yet! You can use the -v flag to read the SOAP response from this tool and get the
information discussed above.
You can always feel free to attempt to launch the image again, but if you run into a persistent
problem (especially with a shared image), you should post to the Amazon EC2 forum.
I ran shutdown from within an ssh session but my instance still shows up as running when I
query it with DescribeInstances and I can't shell into it. What's happening?
This is a "feature" of the shutdown command. If you issue shutdown without a -h (halt) flag it
shuts down the network and switches to single user mode. The instance is still running but without
a network. You should always use shutdown -h when working inside an Amazon EC2 instance.
You can shut the instance down using the TerminateInstances call (ec2-terminate on the
command line).
What username do I use for the various Amazon EC2 tools?
When you sign up with Amazon Web Services, you are given an AWS Account ID. This is your
username. More detail is provided in the Getting Started Guide.
Amazon EC2
Developer Guide
What happens to my running instances if the machines they are running on go down?
The instances themselves will be terminated and will have to be relaunched. The data on the
instances' hard drives will be lost.
Always replicate important data or store it in Amazon S3.
Why do my instances take so long to start?
Amazon EC2 has to move the images around the network before they can be launched. For big
images and/or congested networks, this can take several minutes. Images are cached to alleviate
this problem, so it should be less noticeable as you use your images more frequently.
Why are my instances stuck in a pending state (or a shutting-down state)?
This situation should be rare and is the result of a software error or misconfiguration. We actively
monitor for it, but please let us know if you do encounter this.
I get a "permission denied, wrong user" error when I try to register an image.
Make sure that you are using the correct user ID and certificate to create and upload the image.
You need to use the same ID and certificate to register the image with Amazon EC2.
I get an "InsufficientInstanceCapacity" error when I try to launch an instance.
This error indicates that we don’t currently have enough available capacity to service your
request. During our beta, capacity is limited.
If you are requesting a large number of instances, there may not be enough server capacity to host
them. You could try again at a different time or specify a smaller number of instances to launch.
I get an "InstanceLimitExceeded" error when I try to launch an instance.
This error indicates that you have reached your concurrent running instance limit. For new users
during the public beta, this limit is 20.
If you need additional capacity, please contact us at
How many instances can I launch?
Each user has a concurrent running instance limit. For new users during the public beta, this limit
is 20.
Can I use a static IP in my instances?
No. Your image must be configured as a DHCP client and it will be assigned an IP.
Amazon EC2
Developer Guide
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