One of the most popular new features in ESXi 4.1 is the new Tech Support Mode (abbreviated as TSM). Tech Support Mode is a simple shell for advanced technical support. With situations in which remote scripting tools are not capable of addressing some particular issue, Tech Support Mode provides an alternative. Similar to the way the COS is used to execute diagnostic commands and fix certain low-level problems, Tech Support Mode enables users to view log and configuration files, as well as run certain configuration and utility commands in order to diagnose and fix problems.
Tech Support Mode was actually available since ESXi 3.5. However, it’s use was discouraged unless in consultation with VMware Support. One of the biggest areas of feedback that we received was that people wanted to have the option of a local shell so that they could operate on the host directly at a level below the vSphere APIs for the purpose of troubleshooting and break-fix. Most importantly, they wanted to be able to do this on their own, without requiring any interaction with VMware Support.
VMware heard and responded to this feedback. In ESXi 4.1, Tech Support Mode is fully supported for use by end-users, and is actually enhanced in several ways. In addition to being available on the local console of a host, it can also be accessed remotely through SSH. Access to Tech Support Mode is controlled in the following ways:
- Both local and remote Tech Support Mode can be enabled and disabled separately in both the DCUI and vCenter Server.
- All commands issued in Tech Support Mode are logged through syslog, allowing for a full audit trail. If a syslog server is configured, then this audit trail is automatically included in the remote logging.
- A timeout can be configured for Tech Support Mode (both local and remote), so that after being enabled, it will automatically be disabled after the configured time. Note that existing session won’t be terminated, i.e. if you are already logged in, you won’t get kicked out.
To see various ways to enable and access Tech Support, take a look at this video (thanks to VMware video training author David Davis).
Note that Tech Support Mode is not based on Linux. It is implemented using a specially-compiled version of Busybox, which is a single binary that bundles together various Unix-like utilities, and which is popular with many embedded systems.
To reiterate, Tech Support Mode is recommended for use primarily for support, troubleshooting and break-fix situations. It also can be used as part of a scripted installation, which will be described in a future blog post. All other uses of Tech Support Mode, including running custom scripts, are not recommended for most cases. The “official” policy on Tech Support Mode can be found in this KB article.