sebelk's questions

当我登录时，我有一条“每日消息”，它似乎来自文件 /var/lib/update-notifier/updates-available：

root@ls:~# cat /var/lib/update-notifier/updates-available

95 updates can be applied immediately.
1 of these updates is a standard security update.
To see these additional updates run: apt list --upgradable

但是，当我运行无人值守升级时，它说没有可用的安全更新：

root@ls:~# unattended-upgrades --dry-run -v
Initial blacklisted packages: 
Initial whitelisted packages: 
Starting unattended upgrades script
Allowed origins are: o=Ubuntu,a=bionic, o=Ubuntu,a=bionic-security, o=UbuntuESM,a=bionic
No packages found that can be upgraded unattended and no pending auto-removals

以防万一，这是我的 sources.list 文件：

deb http://archive.ubuntu.com/ubuntu bionic main restricted
deb http://archive.ubuntu.com/ubuntu bionic-updates main restricted
deb http://archive.ubuntu.com/ubuntu bionic universe
deb http://archive.ubuntu.com/ubuntu bionic-updates universe
deb http://archive.ubuntu.com/ubuntu bionic multiverse
deb http://archive.ubuntu.com/ubuntu bionic-updates multiverse
deb http://archive.ubuntu.com/ubuntu bionic-backports main restricted universe multiverse
deb http://archive.ubuntu.com/ubuntu bionic-security main restricted
deb http://archive.ubuntu.com/ubuntu bionic-security universe
deb http://archive.ubuntu.com/ubuntu bionic-security multiverse

编辑 1： apt list-upgradable 的输出

Listing... Done
apt/bionic-updates 1.6.14 amd64 [upgradable from: 1.6.12ubuntu0.2]
apt-utils/bionic-updates 1.6.14 amd64 [upgradable from: 1.6.12ubuntu0.2]
base-files/bionic-updates 10.1ubuntu2.11 amd64 [upgradable from: 10.1ubuntu2.8]
bcache-tools/bionic-updates 1.0.8-2ubuntu0.18.04.1 amd64 [upgradable from: 1.0.8-2build1]
cloud-init/bionic-updates 21.4-0ubuntu1~18.04.1 all [upgradable from: 19.4-33-gbb4131a2-0ubuntu1~18.04.1]
cryptsetup/bionic-updates 2:2.0.2-1ubuntu1.2 amd64 [upgradable from: 2:2.0.2-1ubuntu1.1]
cryptsetup-bin/bionic-updates 2:2.0.2-1ubuntu1.2 amd64 [upgradable from: 2:2.0.2-1ubuntu1.1]
dirmngr/bionic-updates 2.2.4-1ubuntu1.4 amd64 [upgradable from: 2.2.4-1ubuntu1.3]
dmeventd/bionic-updates 2:1.02.145-4.1ubuntu3.18.04.3 amd64 [upgradable from: 2:1.02.145-4.1ubuntu3.18.04.2]
dmsetup/bionic-updates 2:1.02.145-4.1ubuntu3.18.04.3 amd64 [upgradable from: 2:1.02.145-4.1ubuntu3.18.04.2]
dnsmasq-base/bionic-updates 2.79-1ubuntu0.5 amd64 [upgradable from: 2.79-1ubuntu0.4]
friendly-recovery/bionic-updates 0.2.38ubuntu1.2 all [upgradable from: 0.2.38ubuntu1.1]
gnupg/bionic-updates 2.2.4-1ubuntu1.4 amd64 [upgradable from: 2.2.4-1ubuntu1.3]
gnupg-l10n/bionic-updates 2.2.4-1ubuntu1.4 all [upgradable from: 2.2.4-1ubuntu1.3]
gnupg-utils/bionic-updates 2.2.4-1ubuntu1.4 amd64 [upgradable from: 2.2.4-1ubuntu1.3]
gpg/bionic-updates 2.2.4-1ubuntu1.4 amd64 [upgradable from: 2.2.4-1ubuntu1.3]
gpg-agent/bionic-updates 2.2.4-1ubuntu1.4 amd64 [upgradable from: 2.2.4-1ubuntu1.3]
gpg-wks-client/bionic-updates 2.2.4-1ubuntu1.4 amd64 [upgradable from: 2.2.4-1ubuntu1.3]
gpg-wks-server/bionic-updates 2.2.4-1ubuntu1.4 amd64 [upgradable from: 2.2.4-1ubuntu1.3]
gpgconf/bionic-updates 2.2.4-1ubuntu1.4 amd64 [upgradable from: 2.2.4-1ubuntu1.3]
gpgsm/bionic-updates 2.2.4-1ubuntu1.4 amd64 [upgradable from: 2.2.4-1ubuntu1.3]
gpgv/bionic-updates 2.2.4-1ubuntu1.4 amd64 [upgradable from: 2.2.4-1ubuntu1.3]
gzip/bionic-updates 1.6-5ubuntu1.1 amd64 [upgradable from: 1.6-5ubuntu1]
initramfs-tools/bionic-updates 0.130ubuntu3.13 all [upgradable from: 0.130ubuntu3.9]
initramfs-tools-bin/bionic-updates 0.130ubuntu3.13 amd64 [upgradable from: 0.130ubuntu3.9]
initramfs-tools-core/bionic-updates 0.130ubuntu3.13 all [upgradable from: 0.130ubuntu3.9]
iproute2/bionic-updates 4.15.0-2ubuntu1.3 amd64 [upgradable from: 4.15.0-2ubuntu1.1]
kmod/bionic-updates 24-1ubuntu3.5 amd64 [upgradable from: 24-1ubuntu3.2]
landscape-common/bionic-updates 18.01-0ubuntu3.5 amd64 [upgradable from: 18.01-0ubuntu3.4]
libapt-inst2.0/bionic-updates 1.6.14 amd64 [upgradable from: 1.6.12ubuntu0.2]
libapt-pkg5.0/bionic-updates 1.6.14 amd64 [upgradable from: 1.6.12ubuntu0.2]
libaudit-common/bionic-updates 1:2.8.2-1ubuntu1.1 all [upgradable from: 1:2.8.2-1ubuntu1]
libaudit1/bionic-updates 1:2.8.2-1ubuntu1.1 amd64 [upgradable from: 1:2.8.2-1ubuntu1]
libc-bin/bionic-updates 2.27-3ubuntu1.4 amd64 [upgradable from: 2.27-3ubuntu1.2]
libc6/bionic-updates 2.27-3ubuntu1.4 amd64 [upgradable from: 2.27-3ubuntu1.2]
libcryptsetup12/bionic-updates 2:2.0.2-1ubuntu1.2 amd64 [upgradable from: 2:2.0.2-1ubuntu1.1]
libdevmapper-event1.02.1/bionic-updates 2:1.02.145-4.1ubuntu3.18.04.3 amd64 [upgradable from: 2:1.02.145-4.1ubuntu3.18.04.2]
libdevmapper1.02.1/bionic-updates 2:1.02.145-4.1ubuntu3.18.04.3 amd64 [upgradable from: 2:1.02.145-4.1ubuntu3.18.04.2]
libdrm-common/bionic-updates 2.4.101-2~18.04.1 all [upgradable from: 2.4.99-1ubuntu1~18.04.2]
libdrm2/bionic-updates 2.4.101-2~18.04.1 amd64 [upgradable from: 2.4.99-1ubuntu1~18.04.2]
libgnutls30/bionic-updates 3.5.18-1ubuntu1.5 amd64 [upgradable from: 3.5.18-1ubuntu1.3]
libkmod2/bionic-updates 24-1ubuntu3.5 amd64 [upgradable from: 24-1ubuntu3.2]
liblvm2app2.2/bionic-updates 2.02.176-4.1ubuntu3.18.04.3 amd64 [upgradable from: 2.02.176-4.1ubuntu3.18.04.2]
liblvm2cmd2.02/bionic-updates 2.02.176-4.1ubuntu3.18.04.3 amd64 [upgradable from: 2.02.176-4.1ubuntu3.18.04.2]
libnss-systemd/bionic-updates 237-3ubuntu10.53 amd64 [upgradable from: 237-3ubuntu10.50]
libpam-modules/bionic-updates 1.1.8-3.6ubuntu2.18.04.3 amd64 [upgradable from: 1.1.8-3.6ubuntu2.18.04.1]
libpam-modules-bin/bionic-updates 1.1.8-3.6ubuntu2.18.04.3 amd64 [upgradable from: 1.1.8-3.6ubuntu2.18.04.1]
libpam-runtime/bionic-updates 1.1.8-3.6ubuntu2.18.04.3 all [upgradable from: 1.1.8-3.6ubuntu2.18.04.1]
libpam-systemd/bionic-updates 237-3ubuntu10.53 amd64 [upgradable from: 237-3ubuntu10.50]
libpam0g/bionic-updates 1.1.8-3.6ubuntu2.18.04.3 amd64 [upgradable from: 1.1.8-3.6ubuntu2.18.04.1]
libpcap0.8/bionic-updates 1.8.1-6ubuntu1.18.04.2 amd64 [upgradable from: 1.8.1-6ubuntu1.18.04.1]
libssl1.1/bionic-updates 1.1.1-1ubuntu2.1~18.04.14 amd64 [upgradable from: 1.1.1-1ubuntu2.1~18.04.13]
libsystemd0/bionic-updates 237-3ubuntu10.53 amd64 [upgradable from: 237-3ubuntu10.50]
libudev1/bionic-updates 237-3ubuntu10.53 amd64 [upgradable from: 237-3ubuntu10.50]
libxau6/bionic-updates 1:1.0.8-1ubuntu1 amd64 [upgradable from: 1:1.0.8-1]
linux-base/bionic-updates 4.5ubuntu1.7 all [upgradable from: 4.5ubuntu1.2]
linux-firmware/bionic-updates 1.173.20 all [upgradable from: 1.173.18]
locales/bionic-updates 2.27-3ubuntu1.4 all [upgradable from: 2.27-3ubuntu1.2]
lshw/bionic-updates 02.18-0.1ubuntu6.18.04.2 amd64 [upgradable from: 02.18-0.1ubuntu6.18.04.1]
lvm2/bionic-updates 2.02.176-4.1ubuntu3.18.04.3 amd64 [upgradable from: 2.02.176-4.1ubuntu3.18.04.2]
lxcfs/bionic-updates 3.0.3-0ubuntu1~18.04.2 amd64 [upgradable from: 3.0.3-0ubuntu1~18.04.1]
multiarch-support/bionic-updates 2.27-3ubuntu1.4 amd64 [upgradable from: 2.27-3ubuntu1.2]
netplan.io/bionic-updates 0.99-0ubuntu3~18.04.5 amd64 [upgradable from: 0.98-0ubuntu1~18.04.1]
nplan/bionic-updates 0.99-0ubuntu3~18.04.5 all [upgradable from: 0.98-0ubuntu1~18.04.1]
open-iscsi/bionic-updates 2.0.874-5ubuntu2.10 amd64 [upgradable from: 2.0.874-5ubuntu2.7]
open-vm-tools/bionic-updates 2:11.0.5-4ubuntu0.18.04.1 amd64 [upgradable from: 2:11.0.1-2ubuntu0.18.04.2]
openssl/bionic-updates 1.1.1-1ubuntu2.1~18.04.14 amd64 [upgradable from: 1.1.1-1ubuntu2.1~18.04.13]
pollinate/bionic-updates 4.33-0ubuntu1~18.04.2 all [upgradable from: 4.33-0ubuntu1~18.04.1]
python-apt-common/bionic-updates 1.6.5ubuntu0.7 all [upgradable from: 1.6.5ubuntu0.5]
python3-apt/bionic-updates 1.6.5ubuntu0.7 amd64 [upgradable from: 1.6.5ubuntu0.5]
python3-distupgrade/bionic-updates 1:18.04.45 all [upgradable from: 1:18.04.37]
python3-httplib2/bionic-updates 0.9.2+dfsg-1ubuntu0.3 all [upgradable from: 0.9.2+dfsg-1ubuntu0.2]
python3-software-properties/bionic-updates 0.96.24.32.18 all [upgradable from: 0.96.24.32.14]
python3-update-manager/bionic-updates 1:18.04.11.13 all [upgradable from: 1:18.04.11.10]
rsync/bionic-updates 3.1.2-2.1ubuntu1.2 amd64 [upgradable from: 3.1.2-2.1ubuntu1.1]
snapd/bionic-updates 2.51.1+18.04 amd64 [upgradable from: 2.48.3+18.04]
software-properties-common/bionic-updates 0.96.24.32.18 all [upgradable from: 0.96.24.32.14]
sosreport/bionic-updates 4.1-1ubuntu0.18.04.3 amd64 [upgradable from: 3.6-1ubuntu0.18.04.4]
systemd/bionic-updates 237-3ubuntu10.53 amd64 [upgradable from: 237-3ubuntu10.50]
systemd-sysv/bionic-updates 237-3ubuntu10.53 amd64 [upgradable from: 237-3ubuntu10.50]
ubuntu-advantage-tools/bionic-updates 27.5~18.04.1 all [upgradable from: 17]
ubuntu-keyring/bionic-updates 2018.09.18.1~18.04.2 all [upgradable from: 2018.09.18.1~18.04.0]
ubuntu-minimal/bionic-updates 1.417.5 amd64 [upgradable from: 1.417.4]
ubuntu-release-upgrader-core/bionic-updates 1:18.04.45 all [upgradable from: 1:18.04.37]
ubuntu-server/bionic-updates 1.417.5 amd64 [upgradable from: 1.417.4]
ubuntu-standard/bionic-updates 1.417.5 amd64 [upgradable from: 1.417.4]
udev/bionic-updates 237-3ubuntu10.53 amd64 [upgradable from: 237-3ubuntu10.50]
ufw/bionic-updates 0.36-0ubuntu0.18.04.2 all [upgradable from: 0.36-0ubuntu0.18.04.1]
unattended-upgrades/bionic-updates 1.1ubuntu1.18.04.14 all [upgradable from: 1.1ubuntu1.18.04.13]
update-manager-core/bionic-updates 1:18.04.11.13 all [upgradable from: 1:18.04.11.10]

那么谁在说真话，update-notifier-common 还是 unattended-upgrades？ 编辑 2：我想知道“其中一个更新是标准安全更新”在哪里。来自？如何获取此类更新的包名称？

如果运行，我什么也得不到： apt-get upgrade -s | grep ^Inst | grep -i security

我在 cron 手册页上阅读：

Cron 搜索/var/spool/cron以帐户命名的 crontab 文件/etc/passwd；找到的 crontab 被加载到内存中。Cron 还搜索 目录/etc/anacrontab 中的任何文件，这些文件/etc/cron.d具有不同的格式（请参阅 参考资料crontab(5)）。Cron 检查所有存储的 crontab 并检查每个作业以查看它是否需要在当前分钟内运行

然后它说：

/etc/crontab系统 crontab。现在该文件默认为空。最初它通常用于运行每日、每周、每月的作业。默认情况下，这些作业现在通过读取/etc/anacrontab配置文件的 anacron 运行。有关anacrontab(5)更多详细信息，请参阅。

好的，我很清楚如果/etc/crontab为空会发生什么。

我的问题是：如果/etc/crontab存在的话，什么时候读？

注意：手册页来自 CentOS 8。

我想知道 ss 命令输出中某些项目的含义。例如：

# sudo   ss -iepn '( dport = :3443 )'

Netid      State      Recv-Q      Send-Q             Local Address:Port              Peer Address:Port      
tcp        ESTAB      0           0                  192.168.43.39:45486              190.0.2.1:443       users:(("rocketchat-desk",pid=28697,fd=80)) timer:(keepalive,11sec,0) uid:1000 ino:210510085 sk:16f1 <->
         ts sack cubic wscale:7,7 rto:573 rtt:126.827/104.434 ato:40 mss:1388 pmtu:1500 rcvmss:1388 advmss:1448 cwnd:10 bytes_sent:12904 bytes_retrans:385 bytes_acked:12520 bytes_received:13322 segs_out:433 segs_in:444 data_segs_out:215 data_segs_in:253 send 875.5Kbps lastsnd:18722 lastrcv:18723 lastack:18662 pacing_rate 1.8Mbps delivery_rate 298.1Kbps delivered:216 busy:16182ms retrans:0/10 dsack_dups:10 rcv_rtt:305 rcv_space:14480 rcv_ssthresh:6
CLOSE-WAIT      1           0                [2800:810:54a:7f0::1000]:37844                                     [2800:3f0:4002:803::200a]:443                    users:(("plasma-browser-",pid=16020,fd=175)) uid:1000 ino:90761 sk:1d -->
         ts sack cubic wscale:8,7 rto:222 rtt:21.504/5.045 ato:40 mss:1348 pmtu:1500 rcvmss:1208 advmss:1428 cwnd:10 bytes_sent:1470 bytes_acked:1471 bytes_received:11214 segs_out:20 segs_in:20 data_segs_out:8 data_segs_in:13 send 5014881bps lastsnd:96094169 lastrcv:96137280 lastack:96094142 pacing_rate 10029464bps delivery_rate 1363968bps delivered:9 app_limited busy:91ms rcv_space:14280 rcv_ssthresh:64108 minrtt:17.458

主要是 ss 手册页中缺少的项目，我做了一些猜测，如果我错了，请纠正我：

• rcvmss：我不知道是彩信接收
• 建议：？
• 应用程序限制：？
• 忙碌的： ？
• 重新翻译：？
• dsack_dups：重复的段？
• minrtt：在套接字中达到的最小 RTT？

使用该ldd命令时，有一个选项-u, 来

打印未使用的直接依赖项

如在线帮助中所述。

例如：

ldd  -u /bin/gcc
Unused direct dependencies:
        /lib64/libm.so.6
        /lib64/ld-linux-x86-64.so.2

什么是“未使用的直接依赖项”？为什么它们没有被使用？为什么它们是依赖项？

postscreen_dnsbl_reply_mapin postscreen (postfix)是什么意思？我从文档中读到：

如果您的 DNSBL 查询在域名中有“秘密”，您必须从 postscreen(8) SMTP 回复 ( 1 )中审查此信息

从手册：

从包含秘密密码的实际 DNSBL 域名到 postscreen 在拒绝邮件时将回复的 DNSBL 域名的映射。当没有找到映射时，将使用实际的 DNSBL 域。( 2 )

我不明白秘密密码的含义，DNS 域名如何包含密码？

你能给我解释一下吗？