我已经将 Ubuntu 19.10 升级到 20.04，从那时起，它花费的时间明显变长了（大约 2 分钟才能启动）。然而，systemd-analyze显示启动仅需 1 分钟：
Startup finished in 22.428s (kernel) + 1min 3.775s (userspace) = 1min 26.203s
graphical.target reached after 1min 3.627s in userspace
正如其他答案中提到的，我运行dmesg后发现时间戳之间存在很大的时间差距。这里是命令的完整输出，dmesg因为它超出了字符限制。
为了方便起见，我应该指出 3 秒到 21 秒、37 秒到 52 秒、57 秒到 71 秒和 71 秒到 105 秒之间存在差距。这些部分如下：
[ 3.295687] sdb: sdb1
[ 3.298520] sd 4:0:0:1: [sdb] Attached SCSI removable disk
[ 21.385823] EXT4-fs (sda3): mounted filesystem with ordered data mode. Opts: (null)
[ 22.804433] systemd[1]: Inserted module 'autofs4'
[ 37.790817] audit: type=1400 audit(1593936297.560:10): apparmor="STATUS" operation="profile_load" profile="unconfined" name="/usr/lib/cups/backend/cups-pdf" pid=752 comm="apparmor_parser"
[ 37.790820] audit: type=1400 audit(1593936297.560:11): apparmor="STATUS" operation="profile_load" profile="unconfined" name="/usr/sbin/cupsd" pid=752 comm="apparmor_parser"
[ 52.530237] kauditd_printk_skb: 13 callbacks suppressed
[ 52.530240] audit: type=1400 audit(1593936312.300:25): apparmor="DENIED" operation="capable" profile="/usr/sbin/cups-browsed" pid=884 comm="cups-browsed" capability=23 capname="sys_nice"
[ 56.453158] Generic FE-GE Realtek PHY r8169-200:00: attached PHY driver [Generic FE-GE Realtek PHY] (mii_bus:phy_addr=r8169-200:00, irq=IGNORE)
[ 57.951318] RTL871X: cfg80211_rtw_dump_station(wlx00e0202c7613)
[ 57.951319] RTL871X: Station is not found
[ 71.956183] PPP BSD Compression module registered
[ 71.996804] PPP Deflate Compression module registered
[ 105.398067] rfkill: input handler disabled
我在硬盘上安装了 Ubuntu，它是磁盘中唯一的操作系统。检查硬盘后，我没有发现任何减速，它运行正常。Ubuntu 19.10 的启动速度要快得多。启动过程完成后，Ubuntu 运行正常，关机过程也非常快（大约 5 秒）。有没有办法解决这个启动缓慢的问题，而不需要重新安装所有内容？
编辑：
这是命令的输出systemd-analyze blame：
35.198s plymouth-quit-wait.service
16.844s udisks2.service
15.443s networkd-dispatcher.service
15.292s accounts-daemon.service
15.175s systemd-journal-flush.service
12.570s phpsessionclean.service
10.225s apport-autoreport.service
8.504s ModemManager.service
7.997s plymouth-read-write.service
7.200s NetworkManager.service
6.908s dev-sda3.device
6.709s polkit.service
6.434s avahi-daemon.service
5.979s thermald.service
5.978s systemd-logind.service
5.973s wpa_supplicant.service
3.870s apparmor.service
3.841s grub-common.service
3.680s apport.service
3.325s ssh.service
3.157s udhcpd.service
3.106s gdm.service
3.029s gpu-manager.service
3.021s ufw.service
2.924s rsyslog.service
2.148s systemd-modules-load.service
1.969s [email protected]
1.867s systemd-udevd.service
1.732s grub-initrd-fallback.service
1.667s systemd-fsck@dev-disk-by\x2duuid-E766\x2dD5EE.service
1.582s lm-sensors.service
1.203s plymouth-start.service
980ms systemd-tmpfiles-setup-dev.service
976ms colord.service
944ms kerneloops.service
844ms systemd-resolved.service
796ms systemd-udev-trigger.service
763ms systemd-rfkill.service
762ms keyboard-setup.service
761ms systemd-sysusers.service
712ms systemd-tmpfiles-setup.service
676ms [email protected]
675ms systemd-journald.service
607ms upower.service
571ms systemd-sysctl.service
549ms swapfile.swap
528ms binfmt-support.service
509ms systemd-random-seed.service
497ms alsa-restore.service
458ms hddtemp.service
420ms e2scrub_reap.service
384ms boot-efi.mount
347ms pppd-dns.service
342ms systemd-timesyncd.service
264ms openvpn.service
221ms systemd-user-sessions.service
177ms systemd-remount-fs.service
144ms setvtrgb.service
120ms dev-hugepages.mount
119ms dev-mqueue.mount
118ms sys-kernel-debug.mount
118ms sys-kernel-tracing.mount
116ms proc-sys-fs-binfmt_misc.mount
115ms kmod-static-nodes.service
107ms console-setup.service
63ms systemd-update-utmp.service
55ms rtkit-daemon.service
20ms [email protected]
9ms systemd-update-utmp-runlevel.service
2ms sys-fs-fuse-connections.mount
2ms sys-kernel-config.mount
这是命令的输出systemd-analyze critical-chain：
The time when unit became active or started is printed after the "@" character.
The time the unit took to start is printed after the "+" character.
graphical.target @1min 4.202s
└─multi-user.target @1min 4.202s
└─networkd-dispatcher.service @21.522s +15.443s
└─basic.target @21.044s
└─sockets.target @21.044s
└─uuidd.socket @21.044s
└─sysinit.target @20.882s
└─systemd-timesyncd.service @19.201s +342ms
└─systemd-tmpfiles-setup.service @18.486s +712ms
└─systemd-journal-flush.service @3.310s +15.175s
└─systemd-journald.service @2.633s +675ms
└─systemd-journald.socket @2.629s
└─-.mount @2.311s
└─system.slice @2.311s
└─-.slice @2.311s
/var/log/boot.log这些是最近启动的文件内容：
------------ Sun Jul 05 15:56:18 IST 2020 ------------
[ OK ] Listening on Load/Save RF Kill Switch Status /dev/rfkill Watch.
[ OK ] Started Show Plymouth Boot Screen.
[ OK ] Started Forward Password Requests to Plymouth Directory Watch.
[ OK ] Reached target Local Encrypted Volumes.
Starting Load/Save RF Kill Switch Status...
[** ] (1 of 3) A start job is running for Load/Save RF Kill Switch Status (48[ OK ] Found device WDC_WD10EZEX-22MFCA0 EFI\x20System\x20Partition.
Starting File System Check on /dev/disk/by-uuid/E766-D5EE...
[ OK ] Started File System Check Daemon to report status.
[ OK ] Started Load/Save RF Kill Switch Status.
[ OK ] Finished File System Check on /dev/disk/by-uuid/E766-D5EE.
Mounting /boot/efi...
[ OK ] Mounted /boot/efi.
[ OK ] Reached target Local File Systems.
Starting Load AppArmor profiles...
Starting Enable support for additional executable binary formats...
Starting Set console font and keymap...
Starting Tell Plymouth To Write Out Runtime Data...
[ OK ] Finished Set console font and keymap.
Mounting Arbitrary Executable File Formats File System...
[ OK ] Mounted Arbitrary Executable File Formats File System.
[ OK ] Finished Enable support for additional executable binary formats.
[ OK ] Finished Load AppArmor profiles.
[ OK ] Finished Flush Journal to Persistent Storage.
Starting Create Volatile Files and Directories...
[ OK ] Finished Create Volatile Files and Directories.
Starting Network Name Resolution...
Starting Network Time Synchronization...
Starting Update UTMP about System Boot/Shutdown...
[ OK ] Finished Update UTMP about System Boot/Shutdown.
[ OK ] Started Network Time Synchronization.
[ OK ] Reached target System Time Set.
[ OK ] Reached target System Time Synchronized.
[ OK ] Started Network Name Resolution.
[ OK ] Reached target Host and Network Name Lookups.
[ OK ] Finished Tell Plymouth To Write Out Runtime Data.
[ OK ] Reached target System Initialization.
[ OK ] Started ACPI Events Check.
[ OK ] Started Process error reports when automatic reporting is enabled (file watch).
[ OK ] Started CUPS Scheduler.
[ OK ] Started Trigger anacron every hour.
[ OK ] Started Periodic ext4 Online Metadata Check for All Filesystems.
[ OK ] Started Discard unused blocks once a week.
[ OK ] Started Refresh fwupd metadata regularly.
[ OK ] Started Daily rotation of log files.
[ OK ] Started Daily man-db regeneration.
[ OK ] Started Message of the Day.
[ OK ] Started Clean PHP session files every 30 mins.
[ OK ] Started Daily Cleanup of Temporary Directories.
[ OK ] Reached target Paths.
[ OK ] Reached target Timers.
[ OK ] Listening on ACPID Listen Socket.
[ OK ] Listening on Avahi mDNS/DNS-SD Stack Activation Socket.
[ OK ] Listening on CUPS Scheduler.
[ OK ] Listening on D-Bus System Message Bus Socket.
[ OK ] Listening on Erlang Port Mapper Daemon Activation Socket.
[ OK ] Listening on UUID daemon activation socket.
[ OK ] Reached target Sockets.
[ OK ] Reached target Basic System.
Starting Accounts Service...
[ OK ] Started ACPI event daemon.
Starting Save/Restore Sound Card State...
[ OK ] Started Run anacron jobs.
Starting LSB: automatic crash report generation...
Starting Avahi mDNS/DNS-SD Stack...
[ OK ] Started Regular background program processing daemon.
[ OK ] Started CUPS Scheduler.
[ OK ] Started D-Bus System Message Bus.
Starting Network Manager...
[ OK ] Started Save initial kernel messages after boot.
Starting Remove Stale Online ext4 Metadata Check Snapshots...
[ OK ] Reached target Login Prompts.
Starting Detect the available GPUs and deal with any system changes...
Starting LSB: Record successful boot for GRUB...
Starting GRUB failed boot detection...
[ OK ] Started irqbalance daemon.
Starting Initialize hardware monitoring sensors...
Starting Dispatcher daemon for systemd-networkd...
[ OK ] Started Set the CPU Frequency Scaling governor.
Starting Authorization Manager...
Starting Restore /etc/resolv.conf if the system crashed before the ppp link was shut down...
Starting System Logging Service...
Starting Login Service...
Starting Thermal Daemon Service...
Starting LSB: Start busybox udhcpd at boot time...
Starting Disk Manager...
Starting WPA supplicant...
[ OK ] Finished Remove Stale Online ext4 Metadata Check Snapshots.
Starting Clean php session files...
[ OK ] Finished Save/Restore Sound Card State.
[ OK ] Reached target Sound Card.
[ OK ] Finished Restore /etc/resolv.conf if the system crashed before the ppp link was shut down.
[ OK ] Finished GRUB failed boot detection.
[ OK ] Finished Initialize hardware monitoring sensors.
[ OK ] Finished Detect the available GPUs and deal with any system changes.
[ OK ] Started System Logging Service.
[ OK ] Started LSB: Start busybox udhcpd at boot time.
[ OK ] Started LSB: automatic crash report generation.
[ OK ] Started LSB: Record successful boot for GRUB.
答案1
是 Gnome 桌面环境 (GDM) 启动耗时太长了。我已经用 lightDM 替换了 GDM，现在我的系统启动时间不到 30 秒！
关于内核部分，我注意到每当系统异常关闭（例如电源故障）时，内核下次启动需要更多时间。如果系统正常关闭，内核启动时间不到 10 秒。
以下是的当前输出systemd-analyze：
Startup finished in 9.704s (kernel) + 28.376s (userspace) = 38.081s
graphical.target reached after 26.279s in userspace