Tex4066's questions

我正在尝试将 mysql 程序的所有执行（所有表数据、索引等）移动到 RAM 磁盘上，以进行从常规 SSD 中排除文件 IO 的性能实验。

我开始像往常一样安装 mysql sudo apt install mysql-server：. 程序开始，mysqld我可以正常创建数据库。

我还按照此站点上列出的说明创建了一个 RAMDisk：在该位置的 Ubuntu 上创建 RAMDisk/mnt/ramdisk并使用大小25G（我有64G可用的 RAM）。我可以写入这个位置并观察到我的 RAM 开始按应有的方式填满。

现在，我使用以下命令将我的 mysql 库目录复制到此 RAMDisk：

cp -rp /var/lib/mysql /mnt/ramdisk

并符号链接到它，这样我就不必更改文件datadir中的参数/etc/mysql/mysql.conf.d/mysqld.cnf。

mv mysql _mysql    
ln -s /mnt/ramdisk/mysql mysql

我还更改了权限，以便 MySQL“应该”能够访问 RAMDisk：

root@HOSTNAME:/var/lib# ls -l | grep mysql
lrwxrwxrwx  1 mysql         mysql           19 Feb 14 16:45 mysql -> /mnt/ramdisk/mysql/
drwx------  6 mysql         mysql         4096 Feb 14 17:06 _mysql
drwx------  2 mysql         mysql         4096 Feb 14 12:14 mysql-files
drwx------  2 mysql         mysql         4096 Feb 12 17:14 mysql-keyring
drwxr-xr-x  2 root          root          4096 Jan 21 06:10 mysql-upgrade

和

root@HOSTNAME:/mnt# ls -l
total 0
drwxrwxrwt 3 mysql mysql 60 Feb 14 17:24 ramdisk

root@HOSTNAME:/mnt/ramdisk# ls -l
total 0
drwx------ 5 mysql mysql 380 Feb 14 16:41 mysql

但是，当我现在尝试重新启动mysqld程序时，遇到以下错误：

USER@HOSTNAME:/$ sudo /etc/init.d/mysql restart
[sudo] password for USER: 
[....] Restarting mysql (via systemctl): mysql.serviceJob for mysql.service failed because the control process exited with error code.
See "systemctl status mysql.service" and "journalctl -xe" for details.
 failed!

调查两者systemctl status mysql.service，journalctl -xe并没有对问题提供更多见解：

USER@HOSTNAME:/$ systemctl status mysql.service
● mysql.service - MySQL Community Server
   Loaded: loaded (/lib/systemd/system/mysql.service; enabled; vendor preset: enabled)
   Active: failed (Result: exit-code) since Fri 2020-02-14 17:30:55 PST; 1min 0s ago
  Process: 19794 ExecStart=/usr/sbin/mysqld --daemonize --pid-file=/run/mysqld/mysqld.pid (code=exited, status=1/FAILURE)
  Process: 19785 ExecStartPre=/usr/share/mysql/mysql-systemd-start pre (code=exited, status=0/SUCCESS)
 Main PID: 17945 (code=exited, status=0/SUCCESS)

Feb 14 17:30:55 HOSTNAME systemd[1]: mysql.service: Service hold-off time over, scheduling restart.
Feb 14 17:30:55 HOSTNAME systemd[1]: mysql.service: Scheduled restart job, restart counter is at 5.
Feb 14 17:30:55 HOSTNAME systemd[1]: Stopped MySQL Community Server.
Feb 14 17:30:55 HOSTNAME systemd[1]: mysql.service: Start request repeated too quickly.
Feb 14 17:30:55 HOSTNAME systemd[1]: mysql.service: Failed with result 'exit-code'.
Feb 14 17:30:55 HOSTNAME systemd[1]: Failed to start MySQL Community Server.

对于journalctl -xe：

-- Unit mysql.service has begun starting up.
Feb 14 17:30:54 HOSTNAME audit[19792]: AVC apparmor="DENIED" operation="mknod" profile="/usr/sbin/mysqld" name="/mnt/ramdisk/mysql/HOSTNAME.lower-test" pid=19792 comm="mysqld" requested_mask="c" denied_mask="c" fsuid=0 ouid=0
Feb 14 17:30:54 HOSTNAME audit[19792]: AVC apparmor="DENIED" operation="mknod" profile="/usr/sbin/mysqld" name="/mnt/ramdisk/mysql/HOSTNAME.lower-test" pid=19792 comm="mysqld" requested_mask="c" denied_mask="c" fsuid=0 ouid=0
Feb 14 17:30:54 HOSTNAME audit[19792]: AVC apparmor="DENIED" operation="mknod" profile="/usr/sbin/mysqld" name="/mnt/ramdisk/mysql/HOSTNAME.lower-test" pid=19792 comm="mysqld" requested_mask="c" denied_mask="c" fsuid=0 ouid=0
Feb 14 17:30:54 HOSTNAME audit[19796]: AVC apparmor="DENIED" operation="mknod" profile="/usr/sbin/mysqld" name="/mnt/ramdisk/mysql/HOSTNAME.lower-test" pid=19796 comm="mysqld" requested_mask="c" denied_mask="c" fsuid=125 ouid=125
Feb 14 17:30:54 HOSTNAME audit[19796]: AVC apparmor="DENIED" operation="mknod" profile="/usr/sbin/mysqld" name="/mnt/ramdisk/mysql/HOSTNAME.lower-test" pid=19796 comm="mysqld" requested_mask="c" denied_mask="c" fsuid=125 ouid=125
Feb 14 17:30:54 HOSTNAME audit[19796]: AVC apparmor="DENIED" operation="mknod" profile="/usr/sbin/mysqld" name="/mnt/ramdisk/mysql/HOSTNAME.lower-test" pid=19796 comm="mysqld" requested_mask="c" denied_mask="c" fsuid=125 ouid=125
Feb 14 17:30:54 HOSTNAME audit[19796]: AVC apparmor="DENIED" operation="open" profile="/usr/sbin/mysqld" name="/mnt/ramdisk/mysql/ibdata1" pid=19796 comm="mysqld" requested_mask="wr" denied_mask="wr" fsuid=125 ouid=125
Feb 14 17:30:55 HOSTNAME mysqld[19794]: Initialization of mysqld failed: 0
Feb 14 17:30:55 HOSTNAME systemd[1]: mysql.service: Control process exited, code=exited status=1
Feb 14 17:30:55 HOSTNAME systemd[1]: mysql.service: Failed with result 'exit-code'.
Feb 14 17:30:55 HOSTNAME systemd[1]: Failed to start MySQL Community Server.
-- Subject: Unit mysql.service has failed
-- Defined-By: systemd
-- Support: http://www.ubuntu.com/support
-- 
-- Unit mysql.service has failed.

我在通过 SSH 进行 Host-Guest 网络时遇到了一些问题。我在这里查看了许多问题以及 QEMU 的网络文档（https://wiki.qemu.org/Documentation/Networking#How_to_get_SSH_access_to_a_guest），但未能找到答案。

我的来宾 QEMU 实例能够像往常一样通过 SSH 连接到主机。但是，当我尝试从主机通过 SSH 连接到 QEMU 实例时出现ssh_exchange_identification: read: Connection reset by peer错误。

这是我用来启动 QEMU 的命令：

qemu-system-aarch64 -M virt -m 32768 -cpu cortex-a72 \
  -kernel $VMLINUZ \
  -initrd $INITRD \
  -append 'root=/dev/vda2' \
  -drive if=none,file=$COW,format=qcow2,id=hd \
  -device virtio-blk-pci,drive=hd \
  -netdev user,id=mynet \
  -device virtio-net-pci,netdev=mynet \
  -nographic \
  -device e1000,netdev=net0 \
  -netdev user,id=net0,hostfwd=tcp::5555-:22

启动 QEMU 后，我尝试使用以下命令 SSH 并获得以下输出：

<*user*>@<*hostname*>:~$ ssh localhost -p 5555 -vvv
OpenSSH_7.6p1 Ubuntu-4ubuntu0.3, OpenSSL 1.0.2n  7 Dec 2017
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: /etc/ssh/ssh_config line 19: Applying options for *
debug2: resolving "localhost" port 5555
debug2: ssh_connect_direct: needpriv 0
debug1: Connecting to localhost [127.0.0.1] port 5555.
debug1: Connection established.
debug1: identity file /home/<*user*>/.ssh/id_rsa type 0
debug1: key_load_public: No such file or directory
debug1: identity file /home/<*user*>/.ssh/id_rsa-cert type -1
debug1: key_load_public: No such file or directory
debug1: identity file /home/<*user*>/.ssh/id_dsa type -1
debug1: key_load_public: No such file or directory
debug1: identity file /home/<*user*>/.ssh/id_dsa-cert type -1
debug1: key_load_public: No such file or directory
debug1: identity file /home/<*user*>/.ssh/id_ecdsa type -1
debug1: key_load_public: No such file or directory
debug1: identity file /home/<*user*>/.ssh/id_ecdsa-cert type -1
debug1: key_load_public: No such file or directory
debug1: identity file /home/<*user*>/.ssh/id_ed25519 type -1
debug1: key_load_public: No such file or directory
debug1: identity file /home/<*user*>/.ssh/id_ed25519-cert type -1
debug1: Local version string SSH-2.0-OpenSSH_7.6p1 Ubuntu-4ubuntu0.3
ssh_exchange_identification: read: Connection reset by peer

非常感谢您对此的任何帮助！

编辑：

两台机器都运行 Ubuntu 18.04。

主持人：

Linux trace5 5.0.0-37-generic #40~18.04.1-Ubuntu SMP Thu Nov 14 12:06:39 UTC 2019 x86_64 x86_64 x86_64 GNU/Linux

来宾：

Linux qemu-trace 5.2.0-050200-generic #201907072331 SMP Sun Jul 7 23:48:00 UTC 2019 aarch64 aarch64 aarch64 GNU/Linux

来宾正在运行sshd，

ps -ef | grep '[s]shd'
root 616 1 0 Dec11 ? 00:00:00 /usr/sbin/sshd -D

/var/log/auth.log如果有帮助，这是对客人的摘录。我正在阅读身份验证失败，但不确定这意味着什么，因为时间戳与我的主机 ssh-ing 的时间不一致：

Dec 11 18:43:17 qemu-trace sshd[1547]: Server listening on 0.0.0.0 port 22.
Dec 11 18:43:17 qemu-trace sshd[1547]: Server listening on :: port 22.
Dec 11 18:43:17 qemu-trace sudo: pam_unix(sudo:session): session closed for user root
Dec 11 18:45:30 qemu-trace systemd-logind[610]: New seat seat0.
Dec 11 18:45:33 qemu-trace sshd[617]: Server listening on 0.0.0.0 port 22.
Dec 11 18:45:33 qemu-trace sshd[617]: Server listening on :: port 22.
Dec 11 18:46:18 qemu-trace login[620]: pam_unix(login:session): session opened for user trace by LOGIN(uid=0)
Dec 11 18:46:19 qemu-trace systemd-logind[610]: New session 1 of user trace.
Dec 11 18:46:19 qemu-trace systemd: pam_unix(systemd-user:session): session opened for user trace by (uid=0)
Dec 11 19:17:01 qemu-trace CRON[675]: pam_unix(cron:session): session opened for user root by (uid=0)
Dec 11 19:17:02 qemu-trace CRON[675]: pam_unix(cron:session): session closed for user root
Dec 11 19:20:13 qemu-trace systemd-logind[605]: New seat seat0.
Dec 11 19:20:17 qemu-trace sshd[616]: Server listening on 0.0.0.0 port 22.
Dec 11 19:20:17 qemu-trace sshd[616]: Server listening on :: port 22.
Dec 11 19:22:33 qemu-trace login[621]: pam_unix(login:auth): check pass; user unknown
Dec 11 19:22:33 qemu-trace login[621]: pam_unix(login:auth): authentication failure; logname=LOGIN uid=0 euid=0 tty=/dev/ttyAMA0 ruser= rhost=
Dec 11 19:22:37 qemu-trace login[621]: FAILED LOGIN (1) on '/dev/ttyAMA0' FOR 'UNKNOWN', Authentication failure
Dec 11 19:22:49 qemu-trace login[621]: pam_unix(login:session): session opened for user trace by LOGIN(uid=0)
Dec 11 19:22:49 qemu-trace systemd-logind[605]: New session 1 of user trace.
Dec 11 19:22:50 qemu-trace systemd: pam_unix(systemd-user:session): session opened for user trace by (uid=0)