What does mysqld_safe do in my.cnf?

Question

Below is my MySQL config file. I am trying to understand how it works. What is the point of [mysqld_safe]? Hasn't [mysqld] already start MySQL? Why is the log-error and pid-file settings after it?

[mysqld]
# Settings user and group are ignored when systemd is used (fedora >= 15).
# If you need to run mysqld under different user or group, 
# customize your systemd unit file for mysqld according to the
# instructions in http://fedoraproject.org/wiki/Systemd
user=mysql

datadir=/var/lib/mysql
socket=/var/lib/mysql/mysql.sock

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

# Semisynchronous Replication
# http://dev.mysql.com/doc/refman/5.5/en/replication-semisync.html
# uncomment next line on MASTER
;plugin-load=rpl_semi_sync_master=semisync_master.so
# uncomment next line on SLAVE
;plugin-load=rpl_semi_sync_slave=semisync_slave.so

# Others options for Semisynchronous Replication
;rpl_semi_sync_master_enabled=1
;rpl_semi_sync_master_timeout=10
;rpl_semi_sync_slave_enabled=1

# http://dev.mysql.com/doc/refman/5.5/en/performance-schema.html
;performance_schema

innodb_strict_mode=on
sql_mode=TRADITIONAL
;sql_mode=STRICT_TRANS_TABLES,NO_ZERO_DATE,NO_ZERO_IN_DATE
character-set-server=utf8
collation-server=utf8_general_ci

[mysqld_safe]
log-error=/var/log/mysqld.log
pid-file=/var/run/mysqld/mysqld.pid

Answer 1

You can start MySQL server using either mysqld or mysqld_safe. mysqld_safe may itself try to execute mysqld but also may not. See the documentation (the first result in Google for mysqld_safe, btw):

mysqld_safe is the recommended way to start a mysqld server on Unix and NetWare. mysqld_safe adds some safety features such as restarting the server when an error occurs and logging runtime information to an error log file. NetWare-specific behaviors are listed later in this section.

Section [mysqld_safe] in the configuration file is for settings applied when you use mysqld_safe to start MySQL server instead of mysqld.