Time Machine for Arch Linux

I’ve been using Arch Linux for some years, and it’s still my favorite Linux distribution. The feature that distinguished Arch from others is its rolling release which means there’s no such a thing called version in Arch. Using latest packages in Arch is the norm.

However living on the edge means it’s not quite safe. After I installed a bunch of updates including Gnome Shell 3.28, my XPS 15 laptop had trouble to bring up external monitor. It even froze when I plug the HDMI in hot.

I tried to revert some packages like

sudo pacman -U /var/cache/packman/pkg/some-package-1.0.xx.pkg.tar.xz

But it didn’t solve the problem because there were hundreds of packages in last update.

Almost going to panic, I found this instruction to revert all packages to a snapshot in time. And it actually worked wonders for me.

Only surprise is when downgrading packages, I saw errors like

 package-name: /path/to/package-file exists in filesystem

Guess it’s a safe guarding mechanism of pacman but since I know what I was doing so I simply deleted those files. The final command is

sudo pacman -Syyuu

which will bring Arch Linux back to a point of time and the issue has been fixed 🙂

Get access to a container in Kubernetes cluster

With Kubernetes(K8s), there’s no need to do ssh [email protected] anymore since everything is running as containers. There are still occasions when I need shell access to a container to do some troubleshooting.

With Docker I can do

docker exec -ti <container_id> /bin/bash

It’s quite similar in K8s

kubectl exec -ti <container_id> -- /bin/bash

However in K8s containers have random IDs so I need to know the container ID first

kubectl get pods

Then I can grab the container ID and do the `kubectl exec` command. This is hard to automate because picking up the expected container ID using `grep` and `awk` commands can fail if the matching condition is too strict.

Given a deployment like this

apiVersion: extensions/v1beta1
kind: Deployment
 name: my-app-deploy
 replicas: 2
       app: my-app

the K8s way to query the container will be

kubectl get pods --selector=app=my-app -o jsonpath='{.items[0].metadata.name}'

A chained one-liner could be

kubectl exec -ti $(kubectl get pods --selector=app=my-app -o jsonpath='{.items[0].metadata.name}') -- /bin/bash

This doesn’t check for errors, eg. if no container matching `app=my-app` was found, but a better script can be easily crafted from here.


Kops: Add Policies for Migrated Apps

When migrating some old applications to a Kubernetes(k8s) cluster provisioned by kops, a lot of things might break and one of them is the missing policy for the node.

By default, nodes of a k8s cluster have the following permissions:

 // The following permissions are scoped to AWS Route53 HostedZone used to bootstrap the cluster
 // arn:aws:route53:::hostedzone/$hosted_zone_id
 route53:ChangeResourceRecordSets, ListResourceRecordSets, GetHostedZone

Additional policies can be added to the nodes’ role by

kops edit cluster ${CLUSTER_NAME}

Then adding something like:

    node: |
          "Effect": "Allow",
          "Action": ["dynamodb:*"],
          "Resource": ["*"]
          "Effect": "Allow",
          "Action": ["es:*"],
          "Resource": ["*"]

Then it will be effective after:

kops update cluster ${CLUSTER_NAME} --yes

The new policy can be reviewed in AWS IAM console.

Most lines were copied from here: https://github.com/kubernetes/kops/blob/master/docs/iam_roles.md


几个 Linux 小工具

最近很忙, 有几个月没写 blog 了. 顺便写一下最近用到的很顺手的几个小工具, 当然, 都是跟 Linux 相关的.

Mutt 是个 CLI 界面的邮件工具, 我主要用它从程序里发邮件. 安装 mutt 很简单, 直接

apt-get install mutt

即可. mutt 的设置可以写在当前用户的”家”里:

cat ~/.mutt/muttrc
set smtp=”smtp://my.server.com:25/”
set from=”No reply <[email protected]>”

发送邮件的命令相当简单, 很容易和其他软件”串”到一起:

echo “This is the message” |mutt -s “This is the subject” -c “[email protected]” -a /tmp/attachment.txt /tmp/att2.txt — [email protected]

Httpie 是手工调试 HTTP 的好帮手, 而且比 curl 简单很多很多. 你记得住 curl 的那些开关么? 我反正是记不住的.

Pigz 是 gzip 的并行计算版. 我还没做性能测试, 应该不会更慢吧 🙂

Pendulum(钟摆, 这名字用的不错)是个 Python 日期函数库, 是标准函数的人性版, 句法更接近英语.

PS. Linux 25 岁了!