Restore Backup Fails Due to /var/log/wtmp Write Failure on tmpfs with "No space left on device"

Troubleshooting
1

I have searched the existing open and closed issues

Required Information

  • DietPi version | cat /boot/dietpi/.version
    G_DIETPI_VERSION_CORE=9 G_DIETPI_VERSION_SUB=12 G_DIETPI_VERSION_RC=1 G_GITBRANCH=‘master’ G_GITOWNER=‘MichaIng’
  • Distro version | echo $G_DISTRO_NAME $G_RASPBIAN
    bullseye
  • Kernel version | uname --all
    Linux DietPi-iKuai 5.10.0-34-amd64 #1 SMP Debian 5.10.234-1 (2025-02-24) x86_64 GNU/Linux
  • Architecture | dpkg --print-architecture
    amd64
  • SBC model | echo $G_HW_MODEL_NAME
    Native PC (x86_64)
  • Bug report ID | echo $G_HW_UUID
    7ddf35a5-fc4c-402e-863f-397040c17d9d

Additional Information (if applicable)

  • Software title | DietPi-Backup (Restore)
  • Was the software title installed freshly or updated/migrated?
    Backup created from previous DietPi installation, then restoring on same device.
  • Can this issue be replicated on a fresh installation of DietPi?
    Unknown, but issue related to backup restore.

Steps to reproduce

  1. Use DietPi-Backup to restore backup from USB drive (/mnt/usb1/dietpi-backup).
  2. During restore process, rsync fails with error:
    rsync: [receiver] write failed on "/var/log/wtmp": No space left on device (28)
    followed by broken pipe errors.

Expected behaviour

  • Backup restore should complete without errors, especially without “No space left on device” errors.

Actual behaviour

  • Backup restore fails due to “No space left on device” on /var/log/wtmp, despite root filesystem having sufficient free space.
  • /var/log is a tmpfs mounted with limited size (50MB), causing the issue.

Extra details

  • The root cause is /var/log mounted as tmpfs with limited size (51200k). The file /var/log/wtmp exceeded the tmpfs size during restore, causing rsync to fail.
  • Free space on root filesystem was sufficient (>40GB), but tmpfs is independent and limited.
  • Solution: Remount /var/log without tmpfs or increase tmpfs size before restore.

Suggestion

  • For large backups, it is recommended that the restore process temporarily increases the size of the /var/log tmpfs mount or unmounts it to avoid running out of space during restore.
  • Alternatively, provide a warning or check for tmpfs size limits before restore to prevent this error.
2

you are free to change location and size of /var/log according your needs.