ubuntu中/dev/zero是块设备吗

是的，/dev/zero是一个块设备。它是一个特殊的设备文件，可以用于生成一个无限的流数据，其中所有字节都是零。它通常用于初始化内存或磁盘空间，也可以用于测试和调试目的。在Linux系统中，块设备是指可以被分成固定大小块（通常是512字节）的设备，例如硬盘、U盘等。而/dev/zero就是一个虚拟的块设备。

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ubuntu mysql8.0.32 /etc/mysql/my.cnf 文件内容

以下是在Ubuntu系统上安装MySQL 8.0.32后的默认 /etc/mysql/my.cnf 文件内容：

# The MySQL database server configuration file.
#
# You can copy this to one of:
# - "/etc/mysql/my.cnf" to set global options,
# - "~/.my.cnf" to set user-specific options.
# 
# One can use all long options that the program supports.
# Run program with --help to get a list of available options and with
# --print-defaults to see which it would actually understand and use.
#
# For explanations see
# http://dev.mysql.com/doc/mysql/en/server-system-variables.html

[mysqld]
#
# * Basic Settings
#
user                           = mysql
pid-file                       = /var/run/mysqld/mysqld.pid
socket                         = /var/run/mysqld/mysqld.sock
basedir                        = /usr
datadir                        = /var/lib/mysql
tmpdir                         = /tmp
lc-messages-dir                = /usr/share/mysql
#skip-external-locking
skip-name-resolve
skip-host-cache
skip-ssl
sql-mode                       = ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION
log-error                      = /var/log/mysql/error.log

# Disabling symbolic-links is recommended to prevent assorted security risks
symbolic-links=0

# Recommended in standard MySQL setup
# sql_mode=NO_ENGINE_SUBSTITUTION,STRICT_TRANS_TABLES

#
# * Character sets
#
# MySQL/MariaDB default is Latin1, but in Ubuntu UTF-8 is default
#
character-set-server  = utf8mb4
collation-server      = utf8mb4_general_ci

#
# * InnoDB
#
# InnoDB is enabled by default with a 10MB datafile in /var/lib/mysql/.
# Read the manual for more InnoDB related options. There are many!
#

#
# * Security Features
#
# Read the manual, too, if you want chroot!
# chroot = /var/lib/mysql/
#
# For generating SSL certificates you can use for example the GUI tool "tinyca".
#
# ssl-ca=/etc/mysql/cacert.pem
# ssl-cert=/etc/mysql/server-cert.pem
# ssl-key=/etc/mysql/server-key.pem

[mysql]
#
# * Basic Settings
#
socket                         = /var/run/mysqld/mysqld.sock
prompt                         = \u@\h [\d]>\_

[mysqldump]
#
# * Basic Settings
#
socket                         = /var/run/mysqld/mysqld.sock
quick
quote-names
max_allowed_packet             = 16M

[isamchk]
key_buffer                     = 16M

#
# * IMPORTANT: Additional settings that can override those from this file!
#   The files must end with '.cnf', otherwise they'll be ignored.
#
!includedir /etc/mysql/conf.d/

注意，这只是默认的配置文件，实际上你可以根据需要进行修改。

ubuntu18.04设置交换空间

在Ubuntu 18.04上设置交换空间有两种方案，一种是修改原有文件大小，另一种是设置新的交换分区。具体步骤如下：
方案一：修改原有文件大小方式
1. 进入系统根目录：cd /
2. 执行命令：sudo dd if=/dev/zero of=/swap bs=1M count=16384 //每段块1M 共16384块，即16G
3. 执行命令：sudo mkswap /swap // 激活swap空间
4. 执行命令：sudo swapon /swap
5. 使用free -m命令，验证是否设置成功。

方案二：设置新的交换分区
1. 进入系统根目录：cd /
2. 创建一个新的交换分区文件：sudo dd if=/dev/zero of=/swap bs=1M count=16384
3. 创建swap文件系统：sudo mkswap -f swap
4. 开启新的swap：sudo swapon swap
5. 关闭并删除原有的swap文件：sudo swapoff swapfile && sudo rm /swapfile
6. 将/etc/fstab中的swapfile改为swap
7. 使用free -m命令，验证是否设置成功。

永久生效的方法是在/etc/fstab中添加一行：/home/gsc/swapfile/swap none swap defaults 0 0