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// containerd 镜像管理：拉取镜像并创建容器
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package main
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import (
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    "context"
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    "fmt"
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    "log"
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    containerd "github.com/containerd/containerd/v2/client"
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)
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func main() {
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    client, err := containerd.New("/run/containerd/containerd.sock")
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    if err != nil {
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        log.Fatal(err)
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    }
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    defer client.Close()
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    ctx := context.Background()
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    // 拉取镜像
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    image, err := client.Pull(ctx, "docker.io/library/nginx:latest",
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        containerd.WithPullUnpack, // 自动解压
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    )
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    if err != nil {
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        log.Fatal(err)
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    }
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    fmt.Printf("Pulled image: %s\n", image.Name())
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    // 创建容器（只声明镜像与快照，还不涉及运行）
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    container, err := client.NewContainer(ctx, "my-nginx",
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        containerd.WithImage(image),
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        containerd.WithNewSnapshot("my-nginx-snapshot", image),
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        containerd.WithNewSpec(containerd.WithImageConfig(image)),
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    )
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    if err != nil {
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        log.Fatal(err)
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    }
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    defer container.Delete(ctx, containerd.WithSnapshotCleanup)
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}

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# 使用 ctr 命令行操作 containerd
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# 镜像操作
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ctr images pull docker.io/library/nginx:latest
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ctr images list
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ctr images inspect docker.io/library/nginx:latest
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# 容器操作
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ctr containers create docker.io/library/nginx:latest mynginx
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ctr containers list
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# 任务操作
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ctr tasks start mynginx
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ctr tasks list
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ctr tasks kill mynginx
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ctr tasks attach mynginx
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# 快照操作
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ctr snapshots list
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ctr snapshots prepare my-snapshot
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ctr snapshots commit my-snapshot my-committed-snapshot

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# 查看 containerd 的内容存储
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ls /var/lib/containerd/io.containerd.content.v1.content/blobs/sha256/
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# 查看已下载的 blob
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ctr content list
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# 查看快照
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ctr snapshots list

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# 查看 containerd 的 OverlayFS 快照
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ls /var/lib/containerd/io.containerd.snapshotter.v1.overlayfs/
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# 查看快照的元数据
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ctr snapshots list
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# 查看容器的 OverlayFS 挂载
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mount | grep overlay

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# Container 可以没有 Task（已停止的容器）
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ctr containers list
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# NAME       IMAGE
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# mynginx    nginx:latest
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ctr tasks list
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# TASK       PID     STATUS
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# (空：容器未运行)
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# 启动 Task
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ctr tasks start mynginx
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ctr tasks list
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# TASK       PID     STATUS
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# mynginx    12345   RUNNING

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// containerd 的 Task 创建流程（简化）
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func (c *container) NewTask(ctx context.Context, ioCreator IOCreator) (Task, error) {
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    // 1. 获取容器的 rootfs 挂载点
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    mounts, err := c.snapshotter.Mounts(ctx, c.snapshotID)
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    // 2. 准备 OCI Bundle
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    bundle := &Bundle{
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        ID:      c.id,
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        Path:    c.bundlePath,
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        Rootfs:  mounts,
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        Spec:    c.spec,
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    }
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    // 3. 启动 containerd-shim
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    shim, err := shim.Start(ctx, bundle, c.runtime)
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    if err != nil {
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        return nil, err
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    }
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    // 4. 通过 shim 创建 Task
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    task, err := shim.Create(ctx, &task.CreateRequest{
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        ID:       c.id,
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        Bundle:   bundle.Path,
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        Rootfs:   mounts,
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        Terminal: true,
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        Stdin:    "/dev/null",
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        Stdout:   "/dev/null",
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        Stderr:   "/dev/null",
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    })
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    return task, nil
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}

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# 查看 containerd 的插件列表
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ctr plugins list
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# 输出示例：
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# TYPE                            ID             PLATFORMS      STATUS
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# io.containerd.content.v1        content        -              ok
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# io.containerd.snapshotter.v1    overlayfs      linux/amd64    ok
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# io.containerd.diff.v1           walking        linux/amd64    ok
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# io.containerd.runtime.v2        task/shim      -              ok
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# io.containerd.service.v1        diff           -              ok
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# io.containerd.service.v1        images         -              ok
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# io.containerd.service.v1        containers     -              ok
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# io.containerd.service.v1        tasks          -              ok
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# io.containerd.grpc.v1           containers     -              ok
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# io.containerd.grpc.v1           content        -              ok
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# io.containerd.grpc.v1           diff           -              ok
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# io.containerd.grpc.v1           images         -              ok
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# io.containerd.grpc.v1           introspection  -              ok
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# io.containerd.grpc.v1           leases         -              ok
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# io.containerd.grpc.v1           namespaces     -              ok
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# io.containerd.grpc.v1           snapshots      -              ok
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# io.containerd.grpc.v1           tasks          -              ok
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# io.containerd.cri.v1            cri            -              ok

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// 自定义 Snapshotter 插件（简化骨架）
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package mysnapshotter
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import (
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    "context"
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    "github.com/containerd/containerd/v2/plugins/snapshots"
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)
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type mySnapshotter struct {
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    root string
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}
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func NewSnapshotter(root string) snapshots.Snapshotter {
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    return &mySnapshotter{root: root}
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}
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func (s *mySnapshotter) Prepare(ctx context.Context, key, parent string, opts ...snapshots.Opt) ([]mount.Mount, error) {
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    // 创建可写快照
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    return nil, nil
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}
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func (s *mySnapshotter) Commit(ctx context.Context, name, key string, opts ...snapshots.Opt) error {
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    // 提交快照为只读
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    return nil
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}
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func (s *mySnapshotter) Mounts(ctx context.Context, key string) ([]mount.Mount, error) {
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    // 返回挂载点
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    return nil, nil
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}
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func (s *mySnapshotter) Remove(ctx context.Context, key string) error {
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    // 删除快照
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    return nil
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}

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# 订阅 containerd 事件
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ctr events
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# 输出示例：
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# ENVELOPE TIMESTAMP                TOPIC                EVENT
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# 1       2021-08-14T10:00:00Z     /containers/create   {"id":"mynginx",...}
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# 2       2021-08-14T10:00:01Z     /tasks/create        {"id":"mynginx",...}
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# 3       2021-08-14T10:00:01Z     /tasks/start         {"id":"mynginx",...}

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// CRI 事件处理（简化）
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func (c *criService) handleEvent(event *eventtypes.Event) {
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    switch event.Topic {
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    case "/tasks/exit":
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        // 容器退出，更新 Pod 状态
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        c.handleContainerExit(event)
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    case "/tasks/oom":
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        // 容器 OOM，记录事件
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        c.handleContainerOOM(event)
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    }
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}

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package main
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import (
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    "context"
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    "fmt"
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    "log"
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    "os"
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    "syscall"
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    containerd "github.com/containerd/containerd/v2/client"
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    "github.com/containerd/containerd/v2/pkg/namespaces"
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)
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func main() {
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    ctx := namespaces.WithNamespace(context.Background(), "default")
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    client, err := containerd.New("/run/containerd/containerd.sock")
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    if err != nil {
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        log.Fatal(err)
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    }
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    defer client.Close()
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    // 拉取镜像
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    image, err := client.Pull(ctx, "docker.io/library/redis:alpine",
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        containerd.WithPullUnpack,
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    )
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    if err != nil {
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        log.Fatal(err)
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    }
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    fmt.Printf("Pulled: %s\n", image.Name())
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    // 创建容器
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    container, err := client.NewContainer(ctx, "my-redis",
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        containerd.WithImage(image),
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        containerd.WithNewSnapshot("redis-snap", image),
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        containerd.WithNewSpec(
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            containerd.WithImageConfig(image),
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        ),
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    )
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    if err != nil {
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        log.Fatal(err)
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    }
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    defer container.Delete(ctx, containerd.WithSnapshotCleanup)
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    // 创建任务
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    task, err := container.NewTask(ctx, containerd.NewIO(os.Stdin, os.Stdout, os.Stderr))
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    if err != nil {
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        log.Fatal(err)
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    }
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    defer task.Delete(ctx)
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    // 启动任务
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    if err := task.Start(ctx); err != nil {
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        log.Fatal(err)
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    }
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    // 等待退出
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    statusC, err := task.Wait(ctx)
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    if err != nil {
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        log.Fatal(err)
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    }
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    // 发送 SIGTERM
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    task.Kill(ctx, syscall.SIGTERM)
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    status := <-statusC
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    fmt.Printf("Redis exited: %v\n", status)
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}

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# 查看 containerd 日志
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journalctl -u containerd -f
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# 查看 containerd 的 gRPC 调试端点
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curl --unix-socket /run/containerd/containerd.sock http://localhost/v2/
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# 查看容器详情
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ctr containers inspect mynginx
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# 查看任务详情
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ctr tasks inspect mynginx
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# 查看镜像层
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ctr images inspect docker.io/library/nginx:latest | jq .rootfs
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# 查看快照信息
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ctr snapshots inspect mynginx-snap
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# 查看内容信息
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ctr content inspect sha256:abc123...