如果我/etc/clamav/freshclam.conf像这样注释掉 UpdateLogFile 行...
\#UpdateLogFile /var/log/clamav/freshclam.log
...然后我可以运行 sudo freshclam 没问题：
/etc/clamav$ sudo freshclam ClamAV update process started at Mon Feb
6 00:17:07 2017 main.cvd is up to date (version: 57, sigs: 4218790,
f-level: 60, builder: amishhammer) daily.cld is up to date (version:
23009, sigs: 1509149, f-level: 63, builder: neo) bytecode.cld is up to
date (version: 290, sigs: 55, f-level: 63, builder: neo)
但是，如果我取消注释 freshclam.conf 中的 UpdateLogFile 行并运行 sudo freshclam，我会得到：
/etc/clamav$ sudo freshclam
ERROR: Can't open /var/log/clamav/freshclam.log in append mode …