Docker Hub中有很多好用的Docker镜像，但镜像到底如何工作、能做什么、怎么做值得我们研究，如下所示为MySQL官方镜像的docker-entrypoint.sh脚本分析：
#!/bin/bashset -eo pipefailshopt -s nullglob################################################################# 若启动命令时附加了参数，则在参数前添加mysqld，如$0 -f test，则经过此代码处理后，# $@参数变mysqld -f test。其中${1:0:1}从$1参数第0个位置取1字符，如$1为-f，则# 取'-'字符，若条件为真，通过set命令重置$@参数，添加mysqld前缀，即经过处理后$1变# 为mysqld。################################################################# if command starts with an option, prepend mysqldif [ "${1:0:1}" = '-' ]; then set -- mysqld "$@"fi# 解析参数，是否是获取帮助信息参数，并设置wantHelp值###################################################### skip setup if they want an option that stops mysqldwantHelp=for arg; do case "$arg" in -'?'|--help|--print-defaults|-V|--version) wantHelp=1 break ;; esacdone############################## 从文件中读取变量值############################## usage: file_env VAR [DEFAULT]# ie: file_env 'XYZ_DB_PASSWORD' 'example'# (will allow for "$XYZ_DB_PASSWORD_FILE" to fill in the value of# "$XYZ_DB_PASSWORD" from a file, especially for Docker's secrets feature)file_env() { local var="$1" local fileVar="${var}_FILE" local def="${2:-}" if [ "${!var:-}" ] && [ "${!fileVar:-}" ]; then echo >&2 "error: both $var and $fileVar are set (but are exclusive)" exit 1 fi local val="$def" if [ "${!var:-}" ]; then val="${!var}" elif [ "${!fileVar:-}" ]; then val="$(< "${!fileVar}")" fi export "$var"="$val" unset "$fileVar"}############################################################################ 运行mysqld --help --verbose --help 2>&1 >/dev/null命令，# 此命令会检查配置文件，若配置文件没问题，则成功，不成功则输出错误信息，及if中添# 加！取不成功。###########################################################################_check_config() { toRun=( "$@" --verbose --help ) if ! errors="$("${toRun[@]}" 2>&1 >/dev/null)"; then cat >&2 <<-EOM ERROR: mysqld failed while attempting to check config command was: "${toRun[*]}" $errors EOM exit 1 fi}# 1. $1参数为mysqld 以及 wanthelp 参数为空 以及root用户，执行此代码；# 2. _check_config检查配置文件是否正确# 3. 获取DATADIR目录，执行mysqld --verbose --help --log-bin-index=/tmp/tmp.4SyApJWeIo| \# awk '$1 == "'"datadir"'" { print $2; exit }'# 4. 创建并修改目录权限# 5. 执行exec gosu mysql docker-entrypoint.sh "$@"，即重新以mysql用户再次调用脚# 本# allow the container to be started with `--user`if [ "$1" = 'mysqld' -a -z "$wantHelp" -a "$(id -u)" = '0' ]; then _check_config "$@" DATADIR="$(_get_config 'datadir' "$@")" mkdir -p "$DATADIR" chown -R mysql:mysql "$DATADIR" exec gosu mysql "$BASH_SOURCE" "$@"fi# 1. $1参数为mysqld 以及 wanthelp 参数为空，执行此代码，及exec gosu会执行此代码；if [ "$1" = 'mysqld' -a -z "$wantHelp" ]; then# 2. 仍然检查配置文件以及获取datadir目录 # still need to check config, container may have started with --user _check_config "$@" # Get config DATADIR="$(_get_config 'datadir' "$@")"# 3. 若mysql数据库未创建，则执行本段逻辑 if [ ! -d "$DATADIR/mysql" ]; then# 4. 检查是否设置变量，如root密码、允许root密码为空亦或者随机密码 file_env 'MYSQL_ROOT_PASSWORD' if [ -z "$MYSQL_ROOT_PASSWORD" -a -z "$MYSQL_ALLOW_EMPTY_PASSWORD" -a -z "$MYSQL_RANDOM_ROOT_PASSWORD" ]; then echo >&2 'error: database is uninitialized and password option is not specified ' echo >&2 ' You need to specify one of MYSQL_ROOT_PASSWORD, MYSQL_ALLOW_EMPTY_PASSWORD and MYSQL_RANDOM_ROOT_PASSWORD' exit 1 fi# 5. 创建目录 mkdir -p "$DATADIR"# 6. 执行mysqld命令初始化数据库 echo 'Initializing database' "$@" --initialize-insecure echo 'Database initialized'# 7. command -v mysql_ssl_rsa_setup检查命令是否可执行，以及是否存在# server-key.pem文件，若不存在，则生成证书 if command -v mysql_ssl_rsa_setup > /dev/null && [ ! -e "$DATADIR/server-key.pem" ]; then # https://github.com/mysql/mysql-server/blob/23032807537d8dd8ee4ec1c4d40f0633cd4e12f9/packaging/deb-in/extra/mysql-systemd-start#L81-L84 echo 'Initializing certificates' mysql_ssl_rsa_setup --datadir="$DATADIR" echo 'Certificates initialized' fi# 8. 获取socket值并启动mysql SOCKET="$(_get_config 'socket' "$@")" "$@" --skip-networking --socket="${SOCKET}" & pid="$!"# 9. 设置mysql变量（列表形式），而后可以${mysql[@]}调用 mysql=( mysql --protocol=socket -uroot -hlocalhost --socket="${SOCKET}" )# 10. 运行30次，验证mysql是否已经启动完毕 for i in {30..0}; do if echo 'SELECT 1' | "${mysql[@]}" &> /dev/null; then break fi echo 'MySQL init process in progress...' sleep 1 done# 11. 若i为0值，则表明mysql启动失败 if [ "$i" = 0 ]; then echo >&2 'MySQL init process failed.' exit 1 fi# 11. 解决时区bug if [ -z "$MYSQL_INITDB_SKIP_TZINFO" ]; then # sed is for https://bugs.mysql.com/bug.php?id=20545 mysql_tzinfo_to_sql /usr/share/zoneinfo | \ sed 's/Local time zone must be set--see zic manual page/FCTY/' | "${mysql[@]}" mysql fi# 12. 生成root随机密码 if [ ! -z "$MYSQL_RANDOM_ROOT_PASSWORD" ]; then export MYSQL_ROOT_PASSWORD="$(pwgen -1 32)" echo "GENERATED ROOT PASSWORD: $MYSQL_ROOT_PASSWORD" fi# 13. 若MYSQL_ROOT_HOST不为空亦或者不为localhost，则创建root用户 rootCreate= # default root to listen for connections from anywhere file_env 'MYSQL_ROOT_HOST' '%' if [ ! -z "$MYSQL_ROOT_HOST" -a "$MYSQL_ROOT_HOST" != 'localhost' ]; then # no, we don't care if read finds a terminating character in this heredoc # https://unix.stackexchange.com/questions/265149/why-is-set-o-errexit-breaking-this-read-heredoc-expression/265151#265151 read -r -d '' rootCreate <<-EOSQL || true CREATE USER 'root'@'${MYSQL_ROOT_HOST}' IDENTIFIED BY '${MYSQL_ROOT_PASSWORD}' ; GRANT ALL ON *.* TO 'root'@'${MYSQL_ROOT_HOST}' WITH GRANT OPTION ; EOSQL fi# 14. 为'root'@'localhost'重置root密码# 使用$rootCreate创建root "${mysql[@]}" <<-EOSQL -- What's done in this file shouldn't be replicated -- or products like mysql-fabric won't work SET @@SESSION.SQL_LOG_BIN=0; SET PASSWORD FOR 'root'@'localhost'=PASSWORD('${MYSQL_ROOT_PASSWORD}') ; GRANT ALL ON *.* TO 'root'@'localhost' WITH GRANT OPTION ; ${rootCreate} DROP DATABASE IF EXISTS test ; FLUSH PRIVILEGES ; EOSQL# 15. 已设置root密码，故mysql需加上root密码 if [ ! -z "$MYSQL_ROOT_PASSWORD" ]; then mysql+=( -p"${MYSQL_ROOT_PASSWORD}" ) fi# 16. 若配置了MYSQL_DATABASE变量，则创建 file_env 'MYSQL_DATABASE' if [ "$MYSQL_DATABASE" ]; then echo "CREATE DATABASE IF NOT EXISTS \`$MYSQL_DATABASE\` ;" | "${mysql[@]}" mysql+=( "$MYSQL_DATABASE" ) fi# 17. 在数据库内创建用户 file_env 'MYSQL_USER' file_env 'MYSQL_PASSWORD' if [ "$MYSQL_USER" -a "$MYSQL_PASSWORD" ]; then echo "CREATE USER '$MYSQL_USER'@'%' IDENTIFIED BY '$MYSQL_PASSWORD' ;" | "${mysql[@]}" if [ "$MYSQL_DATABASE" ]; then echo "GRANT ALL ON \`$MYSQL_DATABASE\`.* TO '$MYSQL_USER'@'%' ;" | "${mysql[@]}" fi echo 'FLUSH PRIVILEGES ;' | "${mysql[@]}" fi# 18. 执行/docker-entrypoint-initdb.d目录下面的脚本，包含shell、sql echo for f in /docker-entrypoint-initdb.d/*; do case "$f" in *.sh) echo "$0: running $f"; . "$f" ;; *.sql) echo "$0: running $f"; "${mysql[@]}" < "$f"; echo ;; *.sql.gz) echo "$0: running $f"; gunzip -c "$f" | "${mysql[@]}"; echo ;; *) echo "$0: ignoring $f" ;; esac echo done# 19. 设置root密码是否过期 if [ ! -z "$MYSQL_ONETIME_PASSWORD" ]; then "${mysql[@]}" <<-EOSQL ALTER USER 'root'@'%' PASSWORD EXPIRE; EOSQL fi# 20. kill -s TERM "$pid" 杀掉mysql进程，执行成功则返回0，而！kill取反，即kill成# 功后才执行后面的!wait命令 if ! kill -s TERM "$pid" || ! wait "$pid"; then echo >&2 'MySQL init process failed.' exit 1 fi# 21. 初始化成功后，再次启动 echo echo 'MySQL init process done. Ready for start up.' echo fifi# 22. 正式启动数据库exec "$@"