[SOLVED] Executing command through qm guest exec limitations?

[devilkin]

Hi,

I'm currently trying to figure out what's going when executing the following command through qm guest exec:

qm guest exec 110 --timeout 0 -- /bin/bash -c 'docker exec mariadb mysqldump --all-databases -u root -pmyfancypw'

Executing the docker command directly on the guest works, but not via qm guest exec. In the end I get this error:

VM 110 qmp command 'guest-exec-status' failed - got timeout

I'm not entirely sure how the redirection of stdout of the docker exec through the qemu guest agent works. Executing other docker commands works fine.

 

[Moayad]

Hi,

Does the other command work? e.g.:

qm guest exec 110 --timeout 0 -- /bin/bash -c 'docker run hello-world'

 

[devilkin]

Hi,

Does the other command work? e.g.:

qm guest exec 110 --timeout 0 -- /bin/bash -c 'docker run hello-world'

Yep, without issue.

# qm guest exec 110 --timeout 0 -- /bin/bash -c 'docker run hello-world'
{
   "err-data" : "Unable to find image 'hello-world:latest' locally\nlatest: Pulling from library/hello-world\n2db297
10123e: Pulling fs layer\n2db29710123e: Verifying Checksum\n2db29710123e: Download complete\n2db29710123e: Pull comp
lete\nDigest: sha256:2498fce14358aa50ead0cc6c19990fc6ff866ce72aeb5546e1d59caac3d0d60f\nStatus: Downloaded newer imag
e for hello-world:latest\n",
   "exitcode" : 0,
   "exited" : 1,
   "out-data" : "\nHello from Docker!\nThis message shows that your installation appears to be working correctly.\n\
nTo generate this message, Docker took the following steps:\n 1. The Docker client contacted the Docker daemon.\n 2.
 The Docker daemon pulled the \"hello-world\" image from the Docker Hub.\n    (amd64)\n 3. The Docker daemon created
 a new container from that image which runs the\n    executable that produces the output you are currently reading.\
n 4. The Docker daemon streamed that output to the Docker client, which sent it\n    to your terminal.\n\nTo try som
ething more ambitious, you can run an Ubuntu container with:\n $ docker run -it ubuntu bash\n\nShare images, automat
e workflows, and more with a free Docker ID:\n https://hub.docker.com/\n\nFor more examples and ideas, visit:\n http
s://docs.docker.com/get-started/\n\n"
}

 

[devilkin]

I ended up with a different approach:
* Executing the command with output on the VM side, dumping to a local file
* Base64 encoded the file
* Downloaded it using pvesh file-read
* Decode the file

#!/bin/bash

VM_ID=<VM_ID>
NODE_NAME=<node-name>
RETENTION=30
VM_DIR=/var/tmp
DIR=/backupdir

declare -A CONTAINERS

CONTAINERS[container-name]="root-pw"

for CONTAINER in "${!CONTAINERS[@]}"; do
  EXITED=0

  BACKUP_DIR="${DIR}/${CONTAINER}"
  BACKUP_FILE="mysql_${CONTAINER}_$(date '+%F').databases.sql.xz"
  VM_BACKUP_FILE="${BACKUP_FILE}.base64"

  if [ ! -d "${BACKUP_DIR}" ]; then
    mkdir -p "${BACKUP_DIR}"
  fi

  # Start backup to VM disk
  CMD_PID=$(qm guest exec ${VM_ID} --synchronous 0 -- /bin/sh -c "docker exec ${CONTAINER} mysqldump --all-databases -u root -p${CONTAINERS[${CONTAINER}]} | xz | base64 > ${VM_DIR}/${VM_BACKUP_FILE}" | jq -r .pid)

  # Wait for backup to finish
  while [ ${EXITED} -eq 0 ]; do
    read EXITED EXITCODE ERROR < <(qm guest exec-status ${VM_ID} ${CMD_PID} | jq -r '[.exited, .exitcode // 0, ."err-data" // "None"]|@sh')
    sleep 5
  done

  if [ ${EXITCODE} -ne 0 ]; then
    echo "error occurred taking backup: ${ERROR}"
    exit 1
  fi

  # Download backup
  set -o pipefail
  pvesh get /nodes/cube/${NODE_NAME}/${VM_ID}/agent/file-read --output-format json --file ${VM_DIR}/${VM_BACKUP_FILE} 2>/dev/null | jq -r .content | base64 -d > ${BACKUP_DIR}/${BACKUP_FILE}
  if [ ${?} -ne 0 ]; then
    echo "error occurred downloading backup!"
    exit 1
  fi

  # Test backup
  unxz -t ${BACKUP_DIR}/${BACKUP_FILE}
 
  # Delete temporary file 
  read EXITED EXITCODE ERROR < <(qm guest exec ${VM_ID} --timeout=0 -- rm ${VM_DIR}/${VM_BACKUP_FILE} | jq -r '[.exited, .exitcode // 0, ."err-data" // "None"]|@sh')
  if [ ${EXITCODE} -ne 0 ]; then
    echo "error occurred deleting temporary file: ${ERROR}"
    exit 1
  fi
  
  # Cleanup local backup dir
  find ${BACKUP_DIR} -ctime +${RETENTION} -exec rm {} \; 
done