我正在运行 Ubuntu 20.04.6 LTS 服务器。该服务器托管一些 Virtualbox 虚拟机，我每天使用 bash 脚本备份这些虚拟机。这工作得很好。当备份工作时，bash 脚本还会发送一些电子邮件，或者如果备份失败，我会通过电子邮件收到错误消息。
最近我开始收到一些电子邮件，Cron Daemon内容如下：
WARNING: Environment variable LOGNAME or USER does not correspond to effective user id.
主题向我展示了显然导致问题的脚本：Cron <user@server> /home/user/buprod.sh
该脚本是通过 crontab 作为普通用户而不是 root 用户执行的。更令人费解的是，我正在备份多个虚拟机，但我只从一个脚本而不是其他脚本中收到该警告消息。
我需要担心警告消息吗？我怎样才能首先避免它？
编辑（根据评论提供更多信息）：
crontab 位于以下位置var/spool/cron/crontabs/matth并具有以下内容：
# For more information see the manual pages of crontab(5) and cron(8)
# m h dom mon dow command
SHELL=/bin/bash
04 2 * * 1 /home/matth/buproxy.sh
24 2 * * * /home/matth/buprod.sh
导致警告消息的脚本是buprod.sh并且具有以下内容：
#!/bin/bash
# =============== Set your variables here ===============
MYMAIL="[email protected]"
VMDIR="/home/matth/VirtualBox\ VMs/ERPNext\ Production/"
EXPORTDIR="/mnt/video/Backup/vmbackup/"
TEMPDIR="/home/matth/temp/"
VMTMPDIR="/home/matth/temp/ERPNext\ Production/"
LOGDIR="/home/matth/logs/"
LOGNAME="erpnextprod.log"
VM="ERPNext Production"
ERR="nothing"
SECONDS=0
STARTUP=1
COPY=1
# =======================================================
# No manual changes needed below this point
# =======================================================
LOGFILE="$LOGDIR$(date +"%Y-%m-%d-%T")-$LOGNAME"
cdt=$(date)
echo "${cdt}: Backing up VM ${VM}" >> $LOGFILE
# Get the vm state
VMSTATE=$(vboxmanage showvminfo "$VM" --machinereadable | grep "VMState=" | cut -f 2 -d "=")
cdt=$(date)
echo "${cdt}: ${VM}'s state is: ${VMSTATE}." &>> $LOGFILE
# If the VM's state is running or paused, save its state
if [[ $VMSTATE == \"poweroff\" ]]; then
# skip the wait
cdt=$(date)
echo "${cdt}: VM ${VM} is already powered off" &>> $LOGFILE
STARTUP=0
else
# Shut down the VM
cdt=$(date)
echo "${cdt}: Shutting down the VM ${VM}" &>> $LOGFILE
vboxmanage controlvm "$VM" acpipowerbutton
if [ $? -ne 0 ]; then ERR="shutting down"; fi
# cdt=$(date)
# echo "${cdt}: Waiting 120 seconds to let the VM ${VM} shut down" &>> $LOGFILE
# sleep 60s
fi
max_wait=$((SECONDS+120))
cnt=1
# Check state of VM
VMSTATE=$(vboxmanage showvminfo "$VM" --machinereadable | grep "VMState=" | cut -f 2 -d "=")
# Wait a maximum of 120 seconds to avoid an infinite loop in case the VM can't be stopped
while [[ $VMSTATE != \"poweroff\" ]]
do
cdt=$(date)
echo "${cdt}: ${cnt} loop(s) waiting for the VM ${VM} to shut down. Current state is ${VMSTATE}" &>> $LOGFILE
# Wait a few seconds before checking again
sleep 10s
# Checking state of VM again
VMSTATE=$(vboxmanage showvminfo "$VM" --machinereadable | grep "VMState=" | cut -f 2 -d "=")
cnt=$(( $cnt + 1 ))
# If loop has taken more than 60 seconds, break it to avoid an infinite loop
if [ $SECONDS -gt $max_wait ]; then break; fi
done
# Check if VM is now powered off
VMSTATE=$(vboxmanage showvminfo "$VM" --machinereadable | grep "VMState=" | cut -f 2 -d "=")
cdt=$(date)
echo "${cdt}: ${VM}'s state is: ${VMSTATE}." &>> $LOGFILE
if [[ $VMSTATE == \"poweroff\" ]]; then
# First copy it to a local directory to have a faster copy
eval cp -R "${VMDIR}" $TEMPDIR
# eval cp -R "${VMDIR}" $EXPORTDIR
cdt=$(date)
echo "${cdt}: VM ${VM} has been copied from ${VMDIR} to ${TEMPDIR}" &>> $LOGFILE
else
ERR="not powered off"
cdt=$(date)
echo "${cdt}: Not exporting because the VM ${VM} is not powered off." &>> $LOGFILE
COPY=0
fi
if [[ $STARTUP == 1 ]]; then
vboxmanage startvm "$VM" --type headless &>> $LOGFILE
if [ $? -ne 0 ]; then
ERR="starting up"
else
cdt=$(date)
echo "${cdt}: VM is started up again" &>> $LOGFILE
fi
fi
# Calculate duration
duration=$SECONDS
duration="Operation took $(($duration / 60)) minutes, $(($duration % 60)) seconds." &>> $LOGFILE
if [[ $COPY==1 ]]; then
# Now copy off-machine
eval cp -R "${VMTMPDIR}" $EXPORTDIR
cdt=$(date)
echo "${cdt}: VM ${VM} has been copied from ${VMTMPDIR} to ${EXPORTDIR}" &>> $LOGFILE
eval rm -R "${VMTMPDIR}"
cdt=$(date)
echo "${cdt}: Temporary directory ${VMTMPDIR} has been deleted" &>> $LOGFILE
# Calculate duration
duration=$SECONDS
duration="Operation including copy to NAS took $(($duration / 60)) minutes, $(($duration % 60)) seconds." &>> $LOGFI>
fi
# Notify the admin
if [ "$ERR" == "nothing" ]; then
MAILSUBJECT="VM ${VM} succesfully backed up"
MAILBODY="Virtual Machine ${VM} was succesfully backed up!"
MAILBODY="$MAILBODY"$'\n'"$duration"
# MAILBODY=$(echo $MAILBODY && cat $LOGFILE)
else
MAILSUBJECT="Error $ERR VM ${VM}"
MAILBODY="There was an error ${ERR} VM ${VM}."
MAILBODY=$(echo $MAILBODY && cat $LOGFILE)
fi
# Send the mail
echo "$MAILBODY" | mail -s "$MAILSUBJECT" $MYMAIL
编辑 2：提供下面的附加详细信息
我已经检查了脚本生成的日志文件。据了解，该错误似乎来自虚拟机的重新启动。
At 27: USER=, LOGNAME=matth
Fri May 3 11:38:01 AM HKT 2024: Backing up VM XGTERPNext
Fri May 3 11:38:02 AM HKT 2024: XGTERPNext's state is: "running".
Fri May 3 11:38:02 AM HKT 2024: Shutting down the VM XGTERPNext
Fri May 3 11:38:02 AM HKT 2024: 1 loop(s) waiting for the VM XGTERPNext to shut down. Current state is "running"
Fri May 3 11:38:07 AM HKT 2024: XGTERPNext's state is: "poweroff".
Fri May 3 11:38:23 AM HKT 2024: VM XGTERPNext has been copied from /home/matth/VMs/XGTERPNext/ to /home/matth/temp/
At 88: USER=, LOGNAME=matth
WARNING: Environment variable LOGNAME or USER does not correspond to effective user id.
Waiting for VM "XGTERPNext" to power on...
VM "XGTERPNext" has been successfully started.
Fri May 3 11:38:23 AM HKT 2024: VM is started up again
At 98: USER=, LOGNAME=matth
因此，我在该部分之前和之后添加了建议的打印输出，如下所示：
echo "${cdt}: VM ${vm} has been copied from ${vmdir} to ${tempdir}" &>> $logfile
else
err="not powered off"
cdt=$(date)
echo "${cdt}: Not exporting because the VM ${vm} is not powered off." &>> $logfile
fi
echo "At $LINENO: USER=$USER, LOGNAME=$LOGNAME" >> $logfile
if [[ $startup == 1 ]]; then
vboxmanage startvm "$vm" --type headless &>> $logfile
if [ $? -ne 0 ]; then
err="starting up"
else
cdt=$(date)
echo "${cdt}: VM is started up again" >> $logfile
fi
fi
echo "At $LINENO: USER=$USER, LOGNAME=$LOGNAME" >> $logfile
当我在终端中手动运行脚本时，没有警告消息。当脚本通过 crontab 计划运行时，USER 为空，因此与 LOGNAME 不同。
而且，这条警告信息是从4月27日之后才出现的，此前从未出现过。我不确定，但可能我在 4 月 26 日运行了更新，并且发生了一些变化？