To stop having a service automatically start after bootup in a Linux system with systemctl use the following to stop and then disable the service:
sudo systemctl stop service_name sudo systemctl disable service_name
Trying to start the docker service after some upgrades fails with the following message:
Failed to start docker.service: Unit is masked.
It turns out that after upgrading or more specifically removing and then upgrading the docker installation in ubuntu (in this particular case in raspberry 4 with Ubuntu 20.04 installed), results in this error.
A search brings up the following:
https://forums.docker.com/t/failed-to-start-docker-service-unit-is-masked/67413
and from that the following bug post:
https://bugs.launchpad.net/ubuntu/+source/docker.io/+bug/1844894
So the solution is to run the following to be able to start the docker service (described in the first link above):
sudo systemctl unmask docker sudo systemctl start docker
To be able to get a more detailed information about your current linux distribution, including the code names use the following:
kosmas:$ cat /etc/os-release NAME="Ubuntu" VERSION="18.04.5 LTS (Bionic Beaver)" ID=ubuntu ID_LIKE=debian PRETTY_NAME="Ubuntu 18.04.5 LTS" VERSION_ID="18.04" HOME_URL="https://www.ubuntu.com/" SUPPORT_URL="https://help.ubuntu.com/" BUG_REPORT_URL="https://bugs.launchpad.net/ubuntu/" PRIVACY_POLICY_URL="https://www.ubuntu.com/legal/terms-and-policies/privacy-policy" VERSION_CODENAME=bionic UBUNTU_CODENAME=bionic
If you would like to be able to see the dmesg output with timestamps instead of time in seconds since booting up, use the -T like:
dmesg -T | less
There is a very nice example on the O’reilly ‘Linux Under The Hood’ training about using strace to compare performance of two commands that provide the same output but with different calls. The two different commands were: ls and echo *, that they both provide the listing of the current directory.
First using the strace with ls:
kosmas:$ strace -c ls abi-4.13.0-45-generic config-4.4.0-31-generic initrd.img-4.4.0-31-generic System.map-4.15.0-123-generic vmlinuz-4.15.0-123-generic abi-4.13.0-46-generic efi memtest86+.bin System.map-4.15.0-124-generic vmlinuz-4.15.0-124-generic abi-4.4.0-31-generic grub memtest86+.elf System.map-4.15.0-126-generic vmlinuz-4.15.0-126-generic config-4.13.0-45-generic initrd.img-4.13.0-45-generic memtest86+_multiboot.bin System.map-4.4.0-31-generic vmlinuz-4.4.0-31-generic config-4.13.0-46-generic initrd.img-4.13.0-46-generic retpoline-4.13.0-45-generic vmlinuz-4.13.0-45-generic vmlinuz-4.4.0-31-generic.efi.signed config-4.15.0-123-generic initrd.img-4.15.0-123-generic retpoline-4.13.0-46-generic vmlinuz-4.13.0-45-generic.efi.signed config-4.15.0-124-generic initrd.img-4.15.0-124-generic System.map-4.13.0-45-generic vmlinuz-4.13.0-46-generic config-4.15.0-126-generic initrd.img-4.15.0-126-generic System.map-4.13.0-46-generic vmlinuz-4.13.0-46-generic.efi.signed % time seconds usecs/call calls errors syscall ------ ----------- ----------- --------- --------- ---------------- 15.81 0.000095 12 8 write 14.64 0.000088 7 12 mprotect 13.48 0.000081 5 17 mmap 9.98 0.000060 7 9 openat 7.82 0.000047 4 11 close 7.32 0.000044 22 2 getdents 6.82 0.000041 6 7 read 5.66 0.000034 3 10 fstat 4.99 0.000030 4 8 8 access 3.16 0.000019 10 2 2 statfs 2.00 0.000012 12 1 munmap 1.83 0.000011 4 3 brk 1.66 0.000010 5 2 ioctl 1.50 0.000009 5 2 rt_sigaction 0.67 0.000004 4 1 rt_sigprocmask 0.67 0.000004 4 1 arch_prctl 0.67 0.000004 4 1 set_tid_address 0.67 0.000004 4 1 set_robust_list 0.67 0.000004 4 1 prlimit64 0.00 0.000000 0 1 execve ------ ----------- ----------- --------- --------- ---------------- 100.00 0.000601 100 10 total
And using the same with echo *
kosmas:$ strace -c echo * abi-4.13.0-45-generic abi-4.13.0-46-generic abi-4.4.0-31-generic config-4.13.0-45-generic config-4.13.0-46-generic config-4.15.0-123-generic config-4.15.0-124-generic config-4.15.0-126-generic config-4.4.0-31-generic efi grub initrd.img-4.13.0-45-generic initrd.img-4.13.0-46-generic initrd.img-4.15.0-123-generic initrd.img-4.15.0-124-generic initrd.img-4.15.0-126-generic initrd.img-4.4.0-31-generic memtest86+.bin memtest86+.elf memtest86+_multiboot.bin retpoline-4.13.0-45-generic retpoline-4.13.0-46-generic System.map-4.13.0-45-generic System.map-4.13.0-46-generic System.map-4.15.0-123-generic System.map-4.15.0-124-generic System.map-4.15.0-126-generic System.map-4.4.0-31-generic vmlinuz-4.13.0-45-generic vmlinuz-4.13.0-45-generic.efi.signed vmlinuz-4.13.0-46-generic vmlinuz-4.13.0-46-generic.efi.signed vmlinuz-4.15.0-123-generic vmlinuz-4.15.0-124-generic vmlinuz-4.15.0-126-generic vmlinuz-4.4.0-31-generic vmlinuz-4.4.0-31-generic.efi.signed % time seconds usecs/call calls errors syscall ------ ----------- ----------- --------- --------- ---------------- 0.00 0.000000 0 1 read 0.00 0.000000 0 1 write 0.00 0.000000 0 5 close 0.00 0.000000 0 4 fstat 0.00 0.000000 0 6 mmap 0.00 0.000000 0 4 mprotect 0.00 0.000000 0 1 munmap 0.00 0.000000 0 3 brk 0.00 0.000000 0 3 3 access 0.00 0.000000 0 1 execve 0.00 0.000000 0 1 arch_prctl 0.00 0.000000 0 3 openat ------ ----------- ----------- --------- --------- ---------------- 100.00 0.000000 33 3 total
So the difference in time is 0.00000 for the echo and 0.000601 for the ls.
Similarly the number of calls for the echo is 33, but ls is using 100.
You would like to type some sensitive information in the command line (password, key), but you don’t want this to appear in the history.
Add a single space before the start of the command.
To restart your X Window Server from the command line in linux, without affecting any non-graphical programs (but losing any unsaved information in your graphical user interface programs), you can use the following:
sudo systemctl restart display-manager
You would like to have a list of your subdomains for a specific domain (hosted zone), that are hosted in Amazon’s Route 53.
You can install the aws cli docker image from here https://github.com/cgswong/docker-aws if you don’t want to install the aws cli in your computer.
You can afterwards start the container with:
docker run -it cgswong/aws:latestThen configure it by running the following and adding your credentials and zone:
efe9881d4fd:/tmp# aws configure
AWS Access Key ID [None]: aws_access_key_id
AWS Secret Access Key [None]: aws_secret_access_key
Default region name [None]: eu-central-1
Default output format [None]:Then run the first command to get a list of the hosted zones and get the id of the hosted zone you want to find the subdomains for:
3efe9881d4fd:/tmp# aws route53 list-hosted-zones
{
"HostedZones": [
{
"ResourceRecordSetCount": 2,
"CallerReference": "RISWorkflow-RD:xxxxx",
"Config": {
"Comment": "HostedZone created by Route53 Registrar",
"PrivateZone": false
},
"Id": "/hostedzone/HOSTEDZONEID",
"Name": "domain.net."
},
Then pick the HOSTEDZONEID and run the following to get a list of subdomains for that domain:
3efe9881d4fd:/tmp# aws route53 list-resource-record-sets --hosted-zone="HOSTEDZONEID" | grep "Name" | uniq
"Name": "alpah.domain.com.",
"Name": "beta.domain.com.",
"Name": "lamda.domain.com.",
......You would like to have a list of IPs or MAC address for the device in your network
Use the ARP protocol’s command:
$ arp -a
dv1.home (192.168.1.102) at 48:xx:xx:xx:xx:xx [ether] on wlp4s0
dv2.home (192.168.1.127) at a4:xx:xx:xx:xx:xx [ether] on wlp4s0
...
You would like to find out your public IP from the command line without using an online service
Use dig like the following line (taken from https://www.cyberciti.biz/faq/how-to-find-my-public-ip-address-from-command-line-on-a-linux/):
dig +short myip.opendns.com @resolver1.opendns.comyou could also add it as an alias:
alias myip=”dig +short myip.opendns.com @resolver1.opendns.com”