hostd is a critical service running on every VMware ESXi host. It is responsible for managing most of the operations on the host, including but not limited to VM operations, handling vCenter Server connections, and dealing with the vSphere API. If hostd crashes or becomes unresponsive, it can severely impact the operations of the ESXi host.

Common Symptoms of hostd Issues:

1. Inability to connect to the ESXi host using the vSphere Client.
2. VM operations (start, stop, migrate, etc.) fail on the affected host.
3. Errors or disconnects in vCenter when managing the ESXi host.

Possible Reasons for hostd Crashing:

1. Configuration issues.
2. Resource contention on the ESXi host.
3. Corrupt system files or installation.
4. Incompatible hardware or drivers.
5. Bugs in the ESXi version.

Steps to Fix hostd Crashing:

1. Restart Management Agents: The first step is often to try restarting the management agents, including hostd, on the ESXi host.To do this, SSH into the ESXi host and run:

/etc/init.d/hostd restart
/etc/init.d/vpxa restart

1. Check System Resources: Ensure the ESXi host is not running out of critical resources like CPU or memory.
2. Review Logs: Check the hostd logs for any critical errors or warnings. The hostd log is located at /var/log/hostd.log on the ESXi host.

Examples Indicating hostd Issues:

2023-10-06T12:32:01Z [12345] error hostd[7F0ABCDEF123] [Originator@6876 sub=Default] Failed to initialize. Shutting down...

This log entry indicates that hostd failed to initialize a critical component, causing it to shut down.

2023-10-06T12:35:10Z [12346] warning hostd[7F0ABCDEE234] [Originator@6876 sub=ResourceManager] Resource pool memory resources are overcommitted and host memory is running low.

This suggests that the ESXi host’s memory is overcommitted, potentially leading to performance issues or crashes.

Machine Check Exceptions (MCE) are hardware-related errors that typically result from malfunctions in a system’s central processing unit (CPU), memory, or other components. If an ESXi host’s hostd service crashes due to MCE errors, it indicates a potential hardware issue.

When a machine check exception occurs, the system tries to correct the error if possible. If it cannot, the system might crash, and you would typically see evidence of this in the VMkernel logs.

Hypothetical Log Example Indicating MCE Issue:

2023-10-07T11:22:32Z vmkernel: cpu2:12345)MCE: 3456: cpu2: MCA error detected via CMCI (Gbl status=0x0): Restart IP: invalid, Error IP: invalid, MCE in progress
2023-10-07T11:22:32Z vmkernel: cpu2:12345)MCE: 3457: cpu2: MCA error: type=3, channel=4, subchannel=5, rank=1, DIMM=B2, Bank=8, Syndrome=0xdeadbeef, Error: Uncorrected patrol data error
2023-10-07T11:22:32Z vmkernel: cpu2:12345)Panic: 4321: Machine Check Exception: Unable to continue

This log excerpt suggests that the CPU (on cpu2) encountered a machine check exception that it could not correct. The “Uncorrected patrol data error” suggests a potential memory-related issue, possibly with the DIMM in slot B2.

Steps to Handle MCE Errors:

1. Isolate the Affected Hardware: If the log indicates which CPU or memory module is affected, as in the hypothetical example above, you might consider isolating that hardware for further testing.
2. Run Hardware Diagnostics: Use hardware diagnostic tools provided by the server’s manufacturer to check for issues. For many server brands, these tools can test memory, CPU, and other components to identify faults.
3. Check for Overheating: Overheating can cause hardware errors. Ensure the server is adequately cooled, all fans are functioning, and no vents are obstructed.
4. Firmware and Drivers: Ensure that the BIOS, firmware, and hardware drivers are up to date. Sometimes, hardware errors can be resolved or mitigated with firmware updates.
5. Replace Faulty Hardware: If diagnostic tests indicate a hardware fault, replace the faulty component. In the example above, you might consider replacing or reseating the DIMM in slot B2.
6. Engage Vendor Support: If you’re unsure about the error or its implications, engage the support team of your server’s manufacturer. They might have insights into known issues or recommendations specific to your hardware model.
7. Monitor for Recurrence: After taking remediation steps, monitor the system closely to ensure the MCE errors do not recur.