Question

我在CentOS机器的MariaDB上成功运行了这个命令：

MariaDB> select * from foobar into outfile '/tmp/schrodinger_cat.csv'
fields terminated by ',' enclosed by '"' lines terminated by '\n';

Query OK, 900 rows affected (0.06 sec)

猫还活着？否

你期望找到'/tmp/schrodinger_cat.csv'。我也是。我ls：

# ls /tmp/schrodinger_cat.csv

ls: cannot access /tmp/schrodinger_cat.csv: No such file or directory

猫死了？否

什么？所以我回到MariaDB命令行客户端并再次运行相同的SQL：

MariaDB> select * from foobar into outfile '/tmp/schrodinger_cat.csv'
fields terminated by ',' enclosed by '"' lines terminated by '\n';

ERROR 1086 (HY000): File '/tmp/schrodinger_cat.csv' already exists

Cat专属于MariaDB？否

我想也许MariaDB正在访问另一个文件系统？所以我尝试了这个：

MariaDB> \! ls /tmp/schrodinger_cat.csv;

ls: cannot access /tmp/schrodinger_cat.csv: No such file or directory

所以，没有。

知道发生了什么事吗？我如何获得'/tmp/schrodinger_cat.csv'文件？

Answer 1

原来它是MariaDB独有的。

# ls /tmp/systemd-private-*-mariadb.service-*/tmp

/tmp/systemd-private-xxxxxxxxxxxxxxxxxxxxx-mariadb.service-xxx/tmp:
schrodinger_cat.csv

原因是CentOS systemd服务文件集PrivateTmp为true：

[Unit]
Description=MariaDB database server
After=syslog.target
After=network.target

[Service]
Type=simple
User=mysql
Group=mysql

ExecStartPre=/usr/libexec/mariadb-prepare-db-dir %n
# Note: we set --basedir to prevent probes that might trigger SELinux alarms,
# per bug #547485
ExecStart=/usr/bin/mysqld_safe --basedir=/usr
ExecStartPost=/usr/libexec/mariadb-wait-ready $MAINPID

# Give a reasonable amount of time for the server to start up/shut down
TimeoutSec=300

# Place temp files in a secure directory, not /tmp
PrivateTmp=true

[Install]
WantedBy=multi-user.target

您可以从this RedHat blog post找到更多信息。如果PrivateTmp=true，则该流程将包含一个私密的/tmp文件夹。

在一座私人城堡里，这只猫活得很好： - ）

MySQL选择outfile文件“文件已经存在”和“文件不存在”二元性（？）的情况

猫还活着？否

猫死了？否

Cat专属于MariaDB？否

1 个答案: