This page describes tips that you might find helpful if you run into problemsusing Compute Engine.

For help troubleshooting specific issues, see one of the following sections:

• For steps to troubleshoot general issues with instances, such as if yourinstance doesn't start up, seeGeneral troubleshooting.
• For steps to troubleshoot issues with Windows instances, seeTroubleshooting Windows instances.

Viewing different response formats

The Google Cloud CLI performs most of its actions by making RESTAPI calls. The pretty-printed results show only the most important informationreturned by any specific command. To see the different response formats,use the--format flag which displays the response in different output formats,includingjson,yaml, andtext. For example, to see a list of instances inJSON, use--format json:

gcloud compute instances list --format json

Viewing gcloud compute logs

The gcloud CLI creates and stores logs in a log file that youcan query, located at$HOME/.config/gcloud/logs. To see the latest log file ona Linux-based operating system, run:

$less $(find ~/.config/gcloud/logs | sort | tail -n 1)

The log file includes information about all requests and responses made usingthegcloud CLI tool.

To automatically purge the log files created by the gcloud CLI,use themax_log_days property,which sets the maximum number of days to retain log files before deleting.The default setting is 30 days. If you set this property value to 0, it turnsoff log garbage collection and does not delete log files.

 gcloud config set core/max_log_daysDAYS_TO_RETAIN_LOGS

Disable gcloud CLI file logging:

The file$HOME/.config/gcloud/logs consumes space on the local filesystem.The amount of logs generated might overwhelm the amount of space on the localfilesystem, which can cause issues like:

• Space utilization reaching 100% on the instance.
• Failure to execute gcloud CLI logging commands because there isno space left to create a new file on the local filesystem.

To change the gcloud CLI behavior and disable the filelogging, use thedisable_file_loggingproperty:

 gcloud config set core/disable_file_logging True

• The instance has anexternal IPaddress.
• The instance's VPC network uses adefault route whose next hopis the default internet gateway.

Instances can also access the internet indirectly, by connecting throughCloud NAT or an instance-based proxy. For additionalconsiderations, including firewall rule configuration, seeInternet accessrequirements.

Idle connections

Google Cloud VPC networks implement 10-minute connectiontracking for IP protocols that have a concept of aconnection (TCP forexample). This means that inbound packets associated with an establishedconnection are permitted as long as at least one packet is sent or received forthe connection within the last 10 minutes. If no packets for the connectionhave been sent or received for 10 minutes or longer, the idle connection'stracking entries are removed. After the connection's tracking entries have beenremoved, Google Cloud does not permit additional inbound packets until atleast one new outbound packet has been sent. This connection tracking applies toall sources and destinations – bothinternal and external IPaddresses .

To prevent idle connections, do the following:

• Set operating systemTCP keep-alive parameters to a time frame ofless than 10 minutes. This ensures that atleast one packet is sent within the time frame.

• Ensure applications that open TCP connections do so with theSO_KEEPALIVEoption enabled.

The following examples demonstrate how to set operating system TCP keep-aliveparameters with an interval value of one minute. Consult your application orsoftware library's documentation to determine how to configure it to useSO_KEEPALIVE.

$sudo /sbin/sysctl -w net.ipv4.tcp_keepalive_time=60 net.ipv4.tcp_keepalive_intvl=60 net.ipv4.tcp_keepalive_probes=5

$sudo sysctl -w net.inet.tcp.always_keepalive=1 net.inet.tcp.keepidle=60000 net.inet.tcp.keepinit=60000 net.inet.tcp.keepintvl=60000

KeepAliveInterval: 1000KeepAliveTime: 60000TcpMaxDataRetransmissions: 10

Accessing Compute Engine as a different SSH user

By default, thegcloud compute command-line tool uses the$USER variable toadd users to the/etc/passwd file for connecting to virtual machine instancesusing SSH. You can specify a different user using the--ssh-key-file PRIVATE_KEY_FILE flag when running thegcloud compute sshcommand. For example:

gcloud compute ssh example-instance --ssh-key-file my-private-key-file

See thegcloud reference documentation formore information.

Interacting with the serial console

You can enable interactive access to an instance's serial console so you canconnect and troubleshoot instances through the serial console.

To learn more, readInteracting with the Serial Console.

Avoiding packet fragmentation to instances built from custom images

The VPC network has a default maximum transmission unit (MTU)of1460 bytes for Linux images and Windows Server images. However, thenetwork MTU can be changed. For details, see themaximum transmission unit overview in the VPCdocumentation.

When creating client applications that communicate with Compute Engineinstances over UDP sockets, you can avoid fragmentation if you set the maximumsize of the UDP datagram's data to 28 bytes less than the network MTU. Forexample, if the network's MTU is 1460 bytes, you can send up to 1432 bytes ofUDP data per packet without fragmentation. If the network's MTU is 1500 bytes,you can send up to 1472 bytes of UDP data without fragmentation. The 28 bytesare used for an IPv4 packet header (20 bytes) and a UDP datagram header(8 bytes). You can set the network's MTU to a maximum of 8896 bytes.