# atmos toolchain lock

Generate or refresh `toolchain.lock.yaml` for tools already configured in `.tool-versions`, without extracting or installing binaries into the toolchain tree. This is the command to reach for when you've turned on [`toolchain.use_lock_file`](/cli/configuration/toolchain) for an existing project and want to populate the lock file for tools that are already installed — without forcing a full `--reinstall` of every one of them.

## Usage

Execute the `toolchain lock` command like this:

```shell
atmos toolchain lock
```

## Why a Separate Command

`atmos toolchain install` only writes a lock entry as a side effect of actually
installing a tool — and it skips tools that are already installed unless you
pass `--reinstall`. That means turning on `use_lock_file: true` for a project
whose tools were installed before the lock file existed leaves those entries
missing until every tool is forced to reinstall.

`lock` downloads and verifies each tool's artifact — the same way `install`
does, to compute a real checksum — but stops short of extracting or placing a
binary in the toolchain tree. It only writes/updates the tool's
`toolchain.lock.yaml` entry, so it works the same whether the tool is already
installed or not, and never touches an already-installed binary.

## Examples

```shell
# Lock every tool in .tool-versions
atmos toolchain lock

# Lock specific tools
atmos toolchain lock terraform
atmos toolchain lock terraform kubectl

# Limit this batch to two concurrent locks
atmos toolchain lock --max-concurrency 2
```

## Arguments

- **`tool...` (optional)**

  One or more tools to lock. Each tool can be a short name (alias) or full `owner/repo` format.
  If omitted, locks every version configured for every tool in `.tool-versions`.

  Examples: `terraform`, `hashicorp/terraform`, `kubectl`

## Flags

- **`--max-concurrency` (optional)**

  Maximum number of tools to lock concurrently. The default is `4`.
  Use a positive integer; values lower than `1` are rejected. Resolved
  the same way as [`install`'s `--max-concurrency`](/cli/commands/toolchain/install#parallel-install-configuration):
  `--max-concurrency`, `ATMOS_TOOLCHAIN_MAX_CONCURRENCY`, `toolchain.max_concurrency`, then `4`.

## Related Commands

- [`atmos toolchain install`](/cli/commands/toolchain/install) - Install tools from `.tool-versions` (also updates the lock file for tools it installs)
- [`atmos toolchain update`](/cli/commands/toolchain/update) - Move a pinned tool forward to its newest version
- [`atmos toolchain list`](/cli/commands/toolchain/list) - View installed tools and their versions