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这个地震的时候很有用、
看起来很高级的样子，膜拜
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廊坊输气站适应性改造工程
MNS-II低压抽出式开关柜安装调试计划
山东泰开成套电器有限公司
一、 概述 3
二、产品介绍 3
三、调试投运条件 12
四、调试投运计划及时间 12
五、调试投运内容和步骤 12
六、调试所需工器具统计 12
七、备品备件及专用工具 12
MNS-Ⅱ系统是引进瑞士ABB公司制造技术的产品，采用标准模件由工厂组装的低压抽出式开关柜装置，符合IEC60439-1、GB7251.1、JB/T9661、BSEN60439-1、VDE660part-500、UTE63-410等低压电气标准；外壳防护等级引用IEC60529和GB4208标准。适应于交流50（60）HZ、额定工作电压≤660V、额定电流6300A及以下的供配电系统中，作为电能分配、转换、控制和无功功率补偿之用。
MNS-Ⅱ低压开关柜包括固定技术和抽屉技术。选用材料又分钢板结构和塑料结构，骨架及内部安装件均采用敷铝锌板加工；产品技术先进、性能可靠，已经广泛应用于电力、石油、化工、冶金、市政建设、建筑等领域。
二、产品介绍
1.结构特点
柜体采用优质的冷扎钢板或进口的敷铝锌钢板折弯而成，按E=25MM 模数作为最小基本单位，用8.8级自攻锁紧螺钉，组装成各种柜形结构和功能单元。
a.设计紧凑：以较小的空间能容纳较多的功能单元。
b.结构通用性强，组装灵活：以25 mm为摸数的C型型材能满足各种结构形式、防护等级及使用环境的要求。
c.采用标准模块设计：分别可组成保护、操作、转换、控制、调节、测定、指示等标准单元，用户可根据需要任意选用组装。以200余种组装件可以组成不同方案的柜架结构和抽屉单元。
d.安全性：大量采用高强度阻燃型工程塑料组件，有效地加强防护安全性能。
e.技术性能高：主要参数达到当代国际技术水平。
f.压缩场地：三化程度高，可大大压缩储存和运输预制件的场地。
g.装配方便：不需要特殊复杂工具。
2.防护等级
产品外壳防护等级符合IEC529、DIN40050标准：
IP30对大于ф2.5mm固体防护
IP40对大于ф1.0mm固体防护
IP54对尘埃和任意方向喷溅作防护
其他如IP31、IP42、IP43等防护等级根据需要均可作为防护要求来制作。（对大于IP54的防护等级，因防护等级过高，需与制造商协商）。
抽屉在连接、试验、主开关合闸或分闸位置时，其外壳防护等级不变。
３.母线系统
3.1.MNS-Ⅱ型开关柜主母线布置在柜后（柜前侧出线时）或柜顶（后出线时），根据进线需求，可配置一组或二组母线。二组母线可分别采用不同或相同截面的材料，二者即可单独供电，也可并联供电，也可用作后备电源。
3.2.配电母线（垂直母线）组装在封闭的垂直通道中，既可防止电弧引起的放电，又能防止人体接触，通过联接件与主母线联接。
3.3.母线分为三相四线制（A、B、C、PEN）及三相五线制（A、B、C、PE、N）。当采用三相四线制时，PE接地和N中性线不分开，为同一导体PEN；当采用三相五线制时，柜内设有独立的PE接地系统和N中性导体，二者贯穿整个装置，安装在柜前底部及右侧，各回路接地或接零都可就近联接。柜架结构件全部采用自攻螺钉联接，具有较高的接地可靠性。
图一 MNS-Ⅱ母线系统
4.开关柜类型
4.1． 动力中心柜（PC）：采用框架断路器630～6300型断路器
4.2.电动机控制中心柜（MCC）：由大小抽屉组装而成，各回路主开关采用高分断塑壳断路器或旋转式带熔断器的负荷开关。
4.3.功率因数自动补偿柜
（A）主电路柜
（B）电动机控制中心柜
图二、柜型示意图
5.抽屉单元
抽出式开关柜宽度为；抽屉单元安装总高度为72E（E=25mm），每柜最多可装3６个抽屉单元。
抽屉有五种标准尺寸，都是以8E（200mm）高度为基准：
8E/4：在8E高度空间组装4个抽屉单元。
8E/2：在8E高度空间组装2个抽屉单元。
8E：在8E高度空间组装1个抽屉单元。
16E：在16E（400mm）高度空间组装1个抽屉单元。
24E：在24E（600mm）高度空间组装1个抽屉单元。
五种抽屉单元可在一个柜体中作单一组装，也可作混合组装，一个柜体中作单一组装最多容纳抽屉单元数见表1所示。
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查看: 2528|回复: 5
电力电缆的颜色问题
阅读权限30
积分帖子主题
注册海川与360万海川共分享
才可以下载或查看，没有帐号？
uU V W 和地线的颜色有相关规定吗？对应的是黄绿红 蓝？地线是蓝还是黄绿还是黑？？？？
发起有意义的议题
已有&0&人打赏作者
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积分帖子主题
本帖最后由 liuei 于
20:05 编辑
国际标准的地线是黄绿双色线！
国内火线ABC对应的是黄绿红，零线是优先用蓝（没有就用黑）。直流正用棕。
积极参与交流
阅读权限30
积分帖子主题
国际标准的地线是黄绿双色线！
国内火线ABC对应的是黄绿红，零线没有标准，可以是蓝或黑。
liuei 发表于
相关标准是什么？？？？？？三相异步电机应该是接地线还是零线？
阅读权限150
积分帖子主题
大侠霍元甲
& &电机内应该接零线。电机外壳接地线。目的是防止电机绝缘击穿，人员接触时发生触电人身事故。低压供电系统零线地线是短接的。
积极参与交流
阅读权限70
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本帖最后由 liuei 于
19:54 编辑
回复&&大侠霍元甲
& & 低压供电系统零线地线是短接的。
czywqa 发表于
& & 这个不一定的，要看用户的接线方式，前不久去一家工厂做照明系统，试灯时不会亮，查三相电线电压正常，接线正常，可灯就是不会亮，再仔细查才发现这家工厂是用的中性点不接地的低压供电系统，有人错将零线接到了地上！
积极参与交流
阅读权限20
代表ＡＢＣ三相相序
安全漫画（9.9）
安全检查【海川景点猜猜看】开创现代化工先河，化工可能你真的不知道，80年前中国就有了100吨【海川.化工先驱】01范旭东－中国现代盐业【海川闲话】说说你印象深刻的一位老师以及
仪表工都这水平吗，深表怀疑，您也过来瞅瞅，表示不服。大家看看这个帖子我和控制阀的故事（3）-- “我不是专业的……”http://b
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版权所有 海川网-海川化工论坛 -2004Appendix B. Errors, Error Codes, and Common ProblemsAppendix B. Errors, Error Codes, and Common ProblemsTable of Contents
This appendix lists common problems and errors that may occur and
potential resolutions, in addition to listing the errors that may
appear when you call MySQL from any host language. The first section
covers problems and resolutions. Detailed information on errors is
The first list displays server error messages. The second
list displays client program messages.
MySQL Enterprise
The MySQL Enterprise Monitor provides a “Virtual DBA”
to assist with problem solving. For more information, see
B.1. Problems and Common Errors
This section lists some common problems and error messages that
you may encounter. It describes how to determine the causes of the
problems and what to do to solve them.
B.1.1. How to Determine What Is Causing a Problem
When you run into a problem, the first thing you should do is to
find out which program or piece of equipment is causing it:
If you have one of the following symptoms, then it is
probably a hardware problems (such as memory, motherboard,
CPU, or hard disk) or kernel problem:
The keyboard doesn't work. This can normally be checked
by pressing the Caps Lock key. If the Caps Lock light
doesn't change, you have to replace your keyboard.
(Before doing this, you should try to restart your
computer and check all cables to the keyboard.)
The mouse pointer doesn't move.
The machine doesn't answer to a remote machine's pings.
Other programs that are not related to MySQL don't
behave correctly.
Your system restarted unexpectedly. (A faulty user-level
program should never be able to take down your system.)
In this case, you should start by checking all your cables
and run some diagnostic tool to check your hardware! You
should also check whether there are any patches, updates, or
service packs for your operating system that could likely
solve your problem. Check also that all your libraries (such
as glibc) are up to date.
It's always good to use a machine with ECC memory to
discover memory problems early.
If your keyboard is locked up, you may be able to recover by
logging in to your machine from another machine and
executing kbd_mode -a.
Please examine your system log file
(/var/log/messages or similar) for
reasons for your problem. If you think the problem is in
MySQL, you should also examine MySQL's log files. See
If you don't think you have hardware problems, you should
try to find out which program is causing problems. Try using
top, ps, Task Manager,
or some similar program, to check which program is taking
all CPU or is locking the machine.
Use top, df, or a
similar program to check whether you are out of memory, disk
space, file descriptors, or some other critical resource.
If the problem is some runaway process, you can always try
to kill it. If it doesn't want to die, there is probably a
bug in the operating system.
If after you have examined all other possibilities and you have
concluded that the MySQL server or a MySQL client is causing the
problem, it's time to create a bug report for our mailing list
or our support team. In the bug report, try to give a very
detailed description of how the system is behaving and what you
think is happening. You should also state why you think that
MySQL is causing the problem. Take into consideration all the
situations in this chapter. State any problems exactly how they
appear when you examine your system. Use the “copy and
paste” method for any output and error messages from
programs and log files.
Try to describe in detail which program is not working and all
symptoms you see. We have in the past received many bug reports
that state only “the system doesn't work.” This
doesn't provide us with any information about what could be the
If a program fails, it's always useful to know the following
information:
Has the program in question made a segmentation fault (did
it dump core)?
Is the program taking up all available CPU time? Check with
top. Let the program run for a while, it
may simply be evaluating something computationally
intensive.
If the mysqld server is causing problems,
can you get any response from it with mysqladmin -u
root ping or mysqladmin -u root
processlist?
What does a client program say when you try to connect to
the MySQL server? (Try with mysql, for
example.) Does the client jam? Do you get any output from
the program?
When sending a bug report, you should follow the outline
described in .
B.1.2. Common Errors When Using MySQL Programs
This section lists some errors that users frequently encounter
when running MySQL programs. Although the problems show up when
you try to run client programs, the solutions to many of the
problems involves changing the configuration of the MySQL
B.1.2.1. Access denied
An Access denied error can have many
causes. Often the problem is related to the MySQL accounts
that the server allows client programs to use when connecting.
B.1.2.2. Can't connect to [local] MySQL server
A MySQL client on Unix can connect to the
mysqld server in two different ways: By
using a Unix socket file to connect through a file in the
filesystem (default /tmp/mysql.sock), or
by using TCP/IP, which connects through a port number. A Unix
socket file connection is faster than TCP/IP, but can be used
only when connecting to a server on the same computer. A Unix
socket file is used if you don't specify a hostname or if you
specify the special hostname localhost.
If the MySQL server is running on Windows, you can connect via
TCP/IP. If the server is started with the
--enable-named-pipe option, you can also
connect with named pipes if you run the client on the host
where the server is running. The name of the named pipe is
MySQL by default. If you don't give a
hostname when connecting to mysqld, a MySQL
client first tries to connect to the named pipe. If that
doesn't work, it connects to the TCP/IP port. You can force
the use of named pipes on Windows by using
. as the hostname.
The error (2002) Can't connect to ...
normally means that there is no MySQL server running on the
system or that you are using an incorrect Unix socket filename
or TCP/IP port number when trying to connect to the server.
The error (2003) Can't connect to MySQL server on
'server' (10061)
indicates that the network connection has been refused. You
should check that there is a MySQL server running, that it has
network connections enabled, the network port you specified is
the one configured on the server, and that the TCP/IP port you
are using has not been blocked by a firewall or port blocking
Start by checking whether there is a process named
mysqld running on your server host. (Use
ps xa | grep mysqld on Unix or the Task
Manager on Windows.) If there is no such process, you should
start the server. See .
If a mysqld process is running, you can
check it by trying the following commands. The port number or
Unix socket filename might be different in your setup.
host_ip represents the IP number of the
machine where the server is running.
shell& mysqladmin version
shell& mysqladmin variables
shell& mysqladmin -h `hostname` version variables
shell& mysqladmin -h `hostname` --port=3306 version
shell& mysqladmin -h host_ip version
shell& mysqladmin --protocol=SOCKET --socket=/tmp/mysql.sock version
Note the use of backticks rather than forward quotes with the
hostname these cause the output of
hostname (that is, the current hostname) to
be substituted into the mysqladmin command.
If you have no hostname command or are
running on Windows, you can manually type the hostname of your
machine (without backticks) following the
-h option. You can also try -h
127.0.0.1 to connect with TCP/IP to the local host.
Here are some reasons the Can't connect to local
MySQL server error might occur:
mysqld is not running. Check your
operating system's process list to ensure the
mysqld process is present.
You're running a MySQL server on Windows with many TCP/IP
connections to it. If you're experiencing that quite often
your clients get that error, you can find a workaround
You are running on a system that uses MIT-pthreads. If you
are running on a system that doesn't have native threads,
mysqld uses the MIT-pthreads package.
See . However, not all
MIT-pthreads versions support Unix socket files. On a
system without socket file support, you must always
specify the hostname explicitly when connecting to the
server. Try using this command to check the connection to
the server:
shell& mysqladmin -h `hostname` version
Someone has removed the Unix socket file that
mysqld uses
(/tmp/mysql.sock by default). For
example, you might have a cron job that
removes old files from the /tmp
directory. You can always run mysqladmin
version to check whether the Unix socket file
that mysqladmin is trying to use really
exists. The fix in this case is to change the
cron job to not remove
mysql.sock or to place the socket
file somewhere else. See
You have started the mysqld server with
the --socket=/path/to/socket option, but
forgotten to tell client programs the new name of the
socket file. If you change the socket pathname for the
server, you must also notify the MySQL clients. You can do
this by providing the same --socket
option when you run client programs. You also need to
ensure that clients have permission to access the
mysql.sock file. To find out where
the socket file is, you can do:
shell& netstat -ln | grep mysql
You are using Linux and one server thread has died (dumped
core). In this case, you must kill the other
mysqld threads (for example, with
kill or with the
mysql_zap script) before you can
restart the MySQL server. See .
The server or client program might not have the proper
access privileges for the directory that holds the Unix
socket file or the socket file itself. In this case, you
must either change the access privileges for the directory
or socket file so that the server and clients can access
them, or restart mysqld with a
--socket option that specifies a socket
filename in a directory where the server can create it and
where client programs can access it.
If you get the error message Can't connect to MySQL
server on some_host, you can try the following
things to find out what the problem is:
Check whether the server is running on that host by
executing telnet some_host 3306 and
pressing the Enter key a couple of times. (3306 is the
default MySQL port number. Change the value if your server
is listening to a different port.) If there is a MySQL
server running and listening to the port, you should get a
response that includes the server's version number. If you
get an error such as telnet: Unable to connect to
remote host: Connection refused, then there is
no server running on the given port.
If the server is running on the local host, try using
mysqladmin -h localhost variables to
connect using the Unix socket file. Verify the TCP/IP port
number that the server is configured to listen to (it is
the value of the port variable.)
Make sure that your mysqld server was
not started with the --skip-networking
option. If it was, you cannot connect to it using TCP/IP.
Check to make sure that there is no firewall blocking
access to MySQL. Your firewall may be configured on the
basis of the application being executed, or the post
number used by MySQL for communication (3306 by default).
Under Linux or Unix, check your IP tables (or similar)
configuration to ensure that the port has not been
Under Windows, applications such as ZoneAlarm and the
Windows XP personal firewall may need to be configured to
allow external access to a MySQL server.
If you are running under Linux and Security-Enhanced Linux
(SELinux) is enabled, make sure you have disabled SELinux
protection for the mysqld process.
B.1.2.2.1. Connection to MySQL Server Failing on Windows
When you're running a MySQL server on Windows with many
TCP/IP connections to it, and you're experiencing that quite
often your clients get a Can't connect to MySQL
server error, the reason might be that Windows
doesn't allow for enough ephemeral (short-lived) ports to
serve those connections.
By default, Windows allows 5000 ephemeral (short-lived) TCP
ports to the user. After any port is closed it will remain
in a TIME_WAIT status for 120 seconds.
This status allows the connection to be reused at a much
lower cost than reinitializing a brand new connection.
However, the port will not be available again until this
time expires.
With a small stack of available TCP ports (5000) and a high
number of TCP ports being open and closed over a short
period of time along with the TIME_WAIT
status you have a good chance for running out of ports.
There are two ways to address this problem:
Reduce the number of TCP ports consumed quickly by
investigating connection pooling or persistent
connections where possible
Tune some settings in the Windows registry (see below)
IMPORTANT: The following procedure
involves modifying the Windows registry. Before you modify
the registry, make sure to back it up and make sure that you
understand how to restore the registry if a problem occurs.
For information about how to back up, restore, and edit the
registry, view the following article in the Microsoft
Knowledge Base:
Start Registry Editor
(Regedt32.exe).
Locate the following key in the registry:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters
On the Edit menu, click Add
Value, and then add the following registry
Value Name: MaxUserPort
Data Type: REG_DWORD
Value: 65534
This sets the number of ephemeral ports available to any
user. The valid range is between 5000 and 65534
(decimal). The default value is 0x decimal).
On the Edit menu, click Add
Value, and then add the following registry
Value Name: TcpTimedWaitDelay
Data Type: REG_DWORD
This sets the number of seconds to hold a TCP port
connection in TIME_WAIT state before
closing. The valid range is between 0 (zero) and 300
(decimal). The default value is 0x78 (120 decimal).
Quit Registry Editor.
Reboot the machine.
Note: Undoing the above should be as simple as deleting the
registry entries you've created.
B.1.2.3. Lost connection to MySQL server
There are three likely causes for this error message.
Usually it indicates network connectivity trouble and you
should check the condition of your network if this error
occurs frequently. If the error message includes “during
query,” this is probably the case you are experiencing.
Sometimes the “during query” form happens when
millions of rows are being sent as part of one or more
queries. If you know that this is happening, you should try
increasing net_read_timeout from its
default of 30 seconds to 60 seconds or longer, sufficient for
the data transfer to complete.
More rarely, it can happen when the client is attempting the
initial connection to the server. In this case, if your
connect_timeout value is set to only a few
seconds, you may be able to resolve the problem by increasing
it to ten seconds, perhaps more if you have a very long
distance or slow connection. You can determine whether you are
experiencing this more uncommon cause by using SHOW
STATUS LIKE 'aborted_connections'. It will increase
by one for each initial connection attempt that the server
aborts. You may see “reading authorization
packet” as part
if so, that also
suggests that this is the solution that you need.
If the cause is none of those just described, you may be
experiencing a problem with BLOB values
that are larger than max_allowed_packet,
which can cause this error with some clients. Sometime you may
see “packet too large” as part of the error
message, and that confirms that you need to increase
max_allowed_packet.
B.1.2.4. Client does not support authentication protocol
MySQL 5.0 uses an authentication protocol based
on a password hashing algorithm that is incompatible with that
used by older (pre-4.1) clients. If you upgrade the server
from 4.0, attempts to connect to it with an older client may
fail with the following message:
shell& mysql
Client does not support authentication protocol requested
consider upgrading MySQL client
To solve this problem, you should use one of the following
approaches:
Upgrade all client programs to use a 4.1.1 or newer client
When connecting to the server with a pre-4.1 client
program, use an account that still has a pre-4.1-style
Reset the password to pre-4.1 style for each user that
needs to use a pre-4.1 client program. This can be done
using the SET PASSWORD statement and
mysql& SET PASSWORD FOR
-& 'some_user'@'some_host' = OLD_PASSWORD('newpwd');
Alternatively, use UPDATE and
FLUSH PRIVILEGES:
mysql& UPDATE mysql.user SET Password = OLD_PASSWORD('newpwd')
-& WHERE Host = 'some_host' AND User = 'some_user';
mysql& FLUSH PRIVILEGES;
Substitute the password you want to use for
“newpwd” in the
preceding examples. MySQL cannot tell you what the
original password was, so you'll need to pick a new one.
Tell the server to use the older password hashing
algorithm:
Start mysqld with the
--old-passwords option.
Assign an old-format password to each account that has
had its password updated to the longer 4.1 format. You
can identify these accounts with the following query:
mysql& SELECT Host, User, Password FROM mysql.user
-& WHERE LENGTH(Password) & 16;
For each account record displayed by the query, use
the Host and
User values and assign a password
function and either SET PASSWORD or
UPDATE, as described earlier.
In older versions of PHP, the mysql
extension does not support the authentication protocol in
MySQL 4.1.1 and higher. This is true regardless of the PHP
version being used. If you wish to use the
mysql extension with MySQL 4.1 or newer,
you may need to follow one of the options discussed above
for configuring MySQL to work with old clients. The
mysqli extension (stands for "MySQL,
Improved"; added in PHP 5) is compatible with the improved
password hashing employed in MySQL 4.1 and higher, and no
special configuration of MySQL need be done to use this
MySQL client library. For more information about the
mysqli extension, see
It may also be possible to compile the older
mysql extension against the new MySQL
client library. This is beyond the scope of this M
consult the PHP documentation for more information. You also
be able to obtain assistance with these issues in our
For additional background on password hashing and
authentication, see .
B.1.2.5. Password Fails When Entered Interactively
MySQL client programs prompt for a password when invoked with
a --password or -p option
that has no following password value:
shell& mysql -u user_name -p
Enter password:
On some systems, you may find that your password works when
specified in an option file or on the command line, but not
when you enter it interactively at the Enter
password: prompt. This occurs when the library
provided by the system to read passwords limits password
values to a small number of characters (typically eight). That
is a problem with the system library, not with MySQL. To work
around it, change your MySQL password to a value that is eight
or fewer characters long, or put your password in an option
B.1.2.6. Host 'host_name' is
If you get the following error, it means that
mysqld has received many connect requests
from the host
'host_name' that
have been interrupted in the middle:
Host 'host_name' is blocked because of many connection errors.
Unblock with 'mysqladmin flush-hosts'
The number of interrupted connect requests allowed is
determined by the value of the
max_connect_errors system variable. After
max_connect_errors failed requests,
mysqld assumes that something is wrong (for
example, that someone is trying to break in), and blocks the
host from further connections until you execute a
mysqladmin flush-hosts command or issue a
FLUSH HOSTS statement. See
By default, mysqld blocks a host after 10
connection errors. You can adjust the value by starting the
server like this:
shell& mysqld_safe --max_connect_errors=10000 &
If you get this error message for a given host, you should
first verify that there isn't anything wrong with TCP/IP
connections from that host. If you are having network
problems, it does you no good to increase the value of the
max_connect_errors variable.
B.1.2.7. Too many connections
If you get a Too many connections error
when you try to connect to the mysqld
server, this means that all available connections are in use
by other clients.
The number of connections allowed is controlled by the
max_connections system variable. Its
default value is 100. If you need to support more connections,
you should set a larger value for this variable.
MySQL Enterprise
Subscribers to the MySQL Enterprise Monitor receive advice
on dynamically configuring the
max_connections variable — avoiding
failed connection attempts. For more information, see
mysqld actually allows
max_connections+1 clients to connect. The
extra connection is reserved for use by accounts that have the
SUPER privilege. By granting the
SUPER privilege to administrators and not
to normal users (who should not need it), an administrator can
connect to the server and use SHOW
PROCESSLIST to diagnose problems even if the maximum
number of unprivileged clients are connected. See
The maximum number of connections MySQL can support depends on
the quality of the thread library on a given platform. Linux
or Solaris should be able to support 500-1000 simultaneous
connections, depending on how much RAM you have and what your
clients are doing. Static Linux binaries provided by MySQL AB
can support up to 4000 connections.
B.1.2.8. Out of memory
If you issue a query using the mysql client
program and receive an error like the following one, it means
that mysql does not have enough memory to
store the entire query result:
mysql: Out of memory at line 42, 'malloc.c'
mysql: needed 8136 byte (8k), memory in use:
bytes (12189k)
ERROR 2008: MySQL client ran out of memory
To remedy the problem, first check whether your query is
correct. Is it reasonable that it should return so many rows?
If not, correct the query and try again. Otherwise, you can
invoke mysql with the
--quick option. This causes it to use the
function to retrieve the result set, which places less of a
load on the client (but more on the server).
B.1.2.9. MySQL server has gone away
This section also covers the related Lost connection
to server during query error.
The most common reason for the MySQL server has gone
away error is that the server timed out and closed
the connection. In this case, you normally get one of the
following error codes (which one you get is operating
system-dependent):
By default, the server closes the connection after eight hours
if nothing has happened. You can change the time limit by
setting the wait_timeout variable when you
start mysqld. See
If you have a script, you just have to issue the query again
for the client to do an automatic reconnection. This assumes
that you have automatic reconnection in the client enabled
(which is the default for the mysql
command-line client).
Some other common reasons for the MySQL server has
gone away error are:
You (or the db administrator) has killed the running
thread with a KILL statement or a
mysqladmin kill command.
You tried to run a query after closing the connection to
the server. This indicates a logic error in the
application that should be corrected.
A client application running on a different host does not
have the necessary privileges to connect to the MySQL
server from that host.
You got a timeout from the TCP/IP connection on the client
side. This may happen if you have been using the commands:
. In this case
increasing the timeout may help solve the problem.
You have encountered a timeout on the server side and the
automatic reconnection in the client is disabled (the
reconnect flag in the
MYSQL structure is equal to 0).
You are using a Windows client and the server had dropped
the connection (probably because
wait_timeout expired) before the
command was issued.
The problem on Windows is that in some cases MySQL doesn't
get an error from the OS when writing to the TCP/IP
connection to the server, but instead gets the error when
trying to read the answer from the connection.
Prior to MySQL 5.0.19, even if the
reconnect flag in the
MYSQL structure is equal to 1, MySQL
does not automatically reconnect and re-issue the query as
it doesn't know if the server did get the original query
The solution to this is to either do a
connection if there has been a long time since the last
query (this is what MyODBC does) or set
wait_timeout on the
mysqld server so high that it in
practice never times out.
You can also get these errors if you send a query to the
server that is incorrect or too large. If
mysqld receives a packet that is too
large or out of order, it assumes that something has gone
wrong with the client and closes the connection. If you
need big queries (for example, if you are working with big
BLOB columns), you can increase the
query limit by setting the server's
max_allowed_packet variable, which has
a default value of 1MB. You may also need to increase the
maximum packet size on the client end. More information on
setting the packet size is given in
An INSERT or REPLACE
statement that inserts a great many rows can also cause
these sorts of errors. Either one of these statements
sends a single request to the server irrespective of the
number of thus, you can often avoid
the error by reducing the number of rows sent per
INSERT or REPLACE.
You also get a lost connection if you are sending a packet
16MB or larger if your client is older than 4.0.8 and your
server is 4.0.8 and above, or the other way around.
It is also possible to see this error if hostname lookups
fail (for example, if the DNS server on which your server
or network relies goes down). This is because MySQL is
dependent on the host system for name resolution, but has
no way of knowing whether it is working — from
MySQL's point of view the problem is indistinguishable
from any other network timeout.
You may also see the MySQL server has gone
away error if MySQL is started with the
--skip-networking option.
Another networking issue that can cause this error occurs
if the MySQL port (default 3306) is blocked by your
firewall, thus preventing any connections at all to the
MySQL server.
You can also encounter this error with applications that
fork child processes, all of which try to use the same
connection to the MySQL server. This can be avoided by
using a separate connection for each child process.
You have encountered a bug where the server died while
executing the query.
You can check whether the MySQL server died and restarted by
executing mysqladmin version and examining
the server's uptime. If the client connection was broken
because mysqld crashed and restarted, you
should concentrate on finding the reason for the crash. Start
by checking whether issuing the query again kills the server
again. See .
You can get more information about the lost connections by
starting mysqld with the --log-warnings=2
option. This logs some of the disconnected errors in the
hostname.err file. See
If you want to create a bug report regarding this problem, be
sure that you include the following information:
Indicate whether the MySQL server died. You can find
information about this in the server error log. See
If a specific query kills mysqld and
the tables involved were checked with CHECK
TABLE before you ran the query, can you provide
a reproducible test case? See
What is the value of the wait_timeout
system variable in the MySQL server? (mysqladmin
variables gives you the value of this variable.)
Have you tried to run mysqld with the
--log option to determine whether the
problem query appears in the log?
See also , and
B.1.2.10. Packet too large
A communication packet is a single SQL statement sent to the
MySQL server, a single row that is sent to the client, or a
binary log event sent from a master replication server to a
The largest possible packet that can be transmitted to or from
a MySQL 5.0 server or client is 1GB.
When a MySQL client or the mysqld server
receives a packet bigger than
max_allowed_packet bytes, it issues a
Packet too large error and closes the
connection. With some clients, you may also get a
Lost connection to MySQL server during
query error if the communication packet is too
Both the client and the server have their own
max_allowed_packet variable, so if you want
to handle big packets, you must increase this variable both in
the client and in the server.
If you are using the mysql client program,
its default max_allowed_packet variable is
16MB. To set a larger value, start mysql
like this:
shell& mysql --max_allowed_packet=32M
That sets the packet size to 32MB.
The server's default max_allowed_packet
value is 1MB. You can increase this if the server needs to
handle big queries (for example, if you are working with big
BLOB columns). For example, to set the
variable to 16MB, start the server like this:
shell& mysqld --max_allowed_packet=16M
You can also use an option file to set
max_allowed_packet. For example, to set the
size for the server to 16MB, add the following lines in an
option file:
max_allowed_packet=16M
It is safe to increase the value of this variable because the
extra memory is allocated only when needed. For example,
mysqld allocates more memory only when you
issue a long query or when mysqld must
return a large result row. The small default value of the
variable is a precaution to catch incorrect packets between
the client and server and also to ensure that you do not run
out of memory by using large packets accidentally.
You can also get strange problems with large packets if you
are using large BLOB values but have not
given mysqld access to enough memory to
handle the query. If you suspect this is the case, try adding
ulimit -d 256000 to the beginning of the
mysqld_safe script and restarting
B.1.2.11. Communication Errors and Aborted Connections
The server error log can be a useful source of information
about connection problems. See . If
you start the server with the --log-warnings
option, you might find messages like this in your error log:
Aborted connection 854 to db: 'users' user: 'josh'
If Aborted connections messages appear in
the error log, the cause can be any of the following:
The client program did not call
The client had been sleeping more than
wait_timeout or
interactive_timeout seconds without
issuing any requests to the server. See
The client program ended abruptly in the middle of a data
When any of these things happen, the server increments the
Aborted_clients status variable.
The server increments the Aborted_connects
status variable when the following things happen:
A client doesn't have privileges to connect to a database.
A client uses an incorrect password.
A connection packet doesn't contain the right information.
It takes more than connect_timeout
seconds to get a connect packet. See
If these kinds of things happen, it might indicate that
someone is trying to break into your server!
MySQL Enterprise
For reasons of security and performance the advisors
provided by the MySQL Enterprise Monitor pay special
attention to the Aborted_connections
status variable. For more information, see
Other reasons for problems with aborted clients or aborted
connections:
Use of Ethernet protocol with Linux, both half and full
duplex. Many Linux Ethernet drivers have this bug. You
should test for this bug by transferring a huge file via
FTP between the client and server machines. If a transfer
goes in burst-pause-burst-pause mode, you are experiencing
a Linux duplex syndrome. The only solution is switching
the duplex mode for both your network card and hub/switch
to either full duplex or to half duplex and testing the
results to determine the best setting.
Some problem with the thread library that causes
interrupts on reads.
Badly configured TCP/IP.
Faulty Ethernets, hubs, switches, cables, and so forth.
This can be diagnosed properly only by replacing hardware.
The max_allowed_packet variable value
is too small or queries require more memory than you have
allocated for mysqld. See
See also .
B.1.2.12. The table is full
The effective maximum table size for MySQL databases is
usually determined by operating system constraints on file
sizes, not by MySQL internal limits. The following table lists
some examples of operating system file-size limits. This is
only a rough guide and is not intended to be definitive. For
the most up-to-date information, be sure to check the
documentation specific to your operating system.
Windows users, please note that FAT and VFAT (FAT32) are
not considered suitable for production
use with MySQL. Use NTFS instead.
On Linux 2.2, you can get MyISAM tables
larger than 2GB in size by using the Large File Support (LFS)
patch for the ext2 filesystem. Most current Linux
distributions are based on kernel 2.4 or higher and include
all the required LFS patches. On Linux 2.4, patches also exist
for ReiserFS to get support for big files (up to 2TB). With
JFS and XFS, petabyte and larger files are possible on Linux.
For a detailed overview about LFS in Linux, have a look at
Andreas Jaeger's Large File Support in
Linux page at
If you do encounter a full-table error, there are several
reasons why it might have occurred:
The InnoDB storage engine maintains
InnoDB tables within a tablespace that
can be created from several files. This allows a table to
exceed the maximum individual file size. The tablespace
can include raw disk partitions, which allows extremely
large tables. The maximum tablespace size is 64TB.
If you are using InnoDB tables and run
out of room in the InnoDB tablespace.
In this case, the solution is to extend the
InnoDB tablespace. See
You are using MyISAM tables on an
operating system that supports files only up to 2GB in
size and you have hit this limit for the data file or
index file.
You are using a MyISAM table and the
space required for the table exceeds what is allowed by
the internal pointer size. MyISAM
creates data and index table files to allow up to 4GB by
default (256TB as of MySQL 5.0.6), but this limit can be
changed up to the maximum allowable size of 65,536TB
(2567 – 1 bytes).
If you need a MyISAM table that is
larger than the default limit and your operating system
supports large files, the CREATE TABLE
statement supports AVG_ROW_LENGTH and
MAX_ROWS options. See
. The server uses these
options to determine how large a table to allow.
If the pointer size is too small for an existing table,
you can change the options with ALTER
TABLE to increase a table's maximum allowable
size. See .
ALTER TABLE tbl_name MAX_ROWS= AVG_ROW_LENGTH=nnn;
You have to specify AVG_ROW_LENGTH only
for tables with BLOB or
TEXT in this case, MySQL can't
optimize the space required based only on the number of
To change the default size limit for
MyISAM tables, set the
myisam_data_pointer_size, which sets
the number of bytes used for internal row pointers. The
value is used to set the pointer size for new tables if
you do not specify the MAX_ROWS option.
The value of myisam_data_pointer_size
can be from 2 to 7. A value of 4 allows tables up to 4GB;
a value of 6 allows tables up to 256TB.
You can check the maximum data and index sizes by using
this statement:
SHOW TABLE STATUS FROM db_name LIKE 'tbl_name';
You also can use myisamchk -dv
/path/to/table-index-file. See
Other ways to work around file-size limits for
MyISAM tables are as follows:
If your large table is read only, you can use
myisampack to compress it.
myisampack usually compresses a
table by at least 50%, so you can have, in effect,
much bigger tables. myisampack also
can merge multiple tables into a single table. See
MySQL includes a MERGE library that
allows you to handle a collection of
MyISAM tables that have identical
structure as a single MERGE table.
You are using the NDB storage engine,
in which case you need to increase the values for the
DataMemory and
IndexMemory configuration parameters in
your config.ini file. See
You are using the MEMORY
(HEAP) in this case you
need to increase the value of the
max_heap_table_size system variable.
B.1.2.13. Can't create/write to file
If you get an error of the following type for some queries, it
means that MySQL cannot create a temporary file for the result
set in the temporary directory:
Can't create/write to file '\\sqla3fe_0.ism'.
The preceding error is a typical message for W the Unix
message is similar.
One fix is to start mysqld with the
--tmpdir option or to add the option to the
[mysqld] section of your option file. For
example, to specify a directory of
C:\temp, use these lines:
tmpdir=C:/temp
The C:\temp directory must exist and have
sufficient space for the MySQL server to write to. See
Another cause of this error can be permissions issues. Make
sure that the MySQL server can write to the
tmpdir directory.
Check also the error code that you get with
perror. One reason the server cannot write
to a table is that the filesystem is full:
shell& perror 28
OS error code
No space left on device
If you get an error of the following type during startup, it
indicates that the filesystem and/or directory used for
storing data files is write protected. Providing the write
error is to a test file, This error is not serious and can be
safely ignored.
Can't create test file /usr/local/mysql/data/master.lower-testB.1.2.14. Commands out of sync
If you get C you can't run this
command now in your client code, you are calling
client functions in the wrong order.
This can happen, for example, if you are using
and try to
execute a new query before you have called
also happen if you try to execute two queries that return data
without calling
B.1.2.15. Ignoring user
If you get the following error, it means that when
mysqld was started or when it reloaded the
grant tables, it found an account in the
user table that had an invalid password.
Found wrong password for user
'some_user'@'some_host';
ignoring user
As a result, the account is simply ignored by the permission
The following list indicates possible causes of and fixes for
this problem:
You may be running a new version of
mysqld with an old
user table. You can check this by
executing mysqlshow mysql user to see
whether the Password column is shorter
than 16 characters. If so, you can correct this condition
by running the
scripts/add_long_password script.
The account has an old password (eight characters long).
Update the account in the user table to
have a new password.
You have specified a password in the
user table without using the
function. Use
mysql to update the account in the
user table with a new password, making
sure to use the
mysql& UPDATE user SET Password=PASSWORD('newpwd')
-& WHERE User='some_user' AND Host='some_host';
B.1.2.16. Table 'tbl_name' doesn't
If you get either of the following errors, it usually means
that no table exists in the default database with the given
Table 'tbl_name' doesn't exist
Can't find file: 'tbl_name' (errno: 2)
In some cases, it may be that the table does exist but that
you are referring to it incorrectly:
Because MySQL uses directories and files to store
databases and tables, database and table names are case
sensitive if they are located on a filesystem that has
case-sensitive filenames.
Even for filesystems that are not case sensitive, such as
on Windows, all references to a given table within a query
must use the same lettercase.
You can check which tables are in the default database with
SHOW TABLES. See .
B.1.2.17. Can't initialize character set
You might see an error like this if you have character set
MySQL Connection Failed: Can't initialize character set charset_name
This error can have any of the following causes:
The character set is a multi-byte character set and you
have no support for the character set in the client. In
this case, you need to recompile the client by running
configure with the
--with-charset=charset_name
--with-extra-charsets=charset_name
option. See .
All standard MySQL binaries are compiled with
--with-extra-character-sets=complex,
which enables support for all multi-byte character sets.
The character set is a simple character set that is not
compiled into mysqld, and the character
set definition files are not in the place where the client
expects to find them.
In this case, you need to use one of the following methods
to solve the problem:
Recompile the client with support for the character
set. See .
Specify to the client the directory where the
character set definition files are located. For many
clients, you can do this with the
--character-sets-dir option.
Copy the character definition files to the path where
the client expects them to be.
B.1.2.18. 'File' Not Found and
Similar Errors
If you get ERROR '...' not found (errno:
23), Can't open file: ... (errno:
24), or any other error with errno
23 or errno 24 from MySQL, it
means that you haven't allocated enough file descriptors for
the MySQL server. You can use the perror
utility to get a description of what the error number means:
shell& perror 23
OS error code
File table overflow
shell& perror 24
OS error code
Too many open files
shell& perror 11
OS error code
Resource temporarily unavailable
The problem here is that mysqld is trying
to keep open too many files simultaneously. You can either
tell mysqld not to open so many files at
once or increase the number of file descriptors available to
To tell mysqld to keep open fewer files at
a time, you can make the table cache smaller by reducing the
value of the table_cache system variable
(the default value is 64). Reducing the value of
max_connections also reduces the number of
open files (the default value is 100).
To change the number of file descriptors available to
mysqld, you can use the
--open-files-limit option to
mysqld_safe or set the
open_files_limit system variable. See
. The easiest way to
set these values is to add an option to your option file. See
. If you have an old version of
mysqld that doesn't support setting the
open files limit, you can edit the
mysqld_safe script. There is a
commented-out line ulimit -n 256 in the
script. You can remove the “#”
character to uncomment this line, and change the number
256 to set the number of file descriptors
to be made available to mysqld.
--open-files-limit and
ulimit can increase the number of file
descriptors, but only up to the limit imposed by the operating
system. There is also a “hard” limit that can be
overridden only if you start mysqld_safe or
mysqld as root (just
remember that you also need to start the server with the
--user option in this case so that it does
not continue to run as root after it starts
up). If you need to increase the operating system limit on the
number of file descriptors available to each process, consult
the documentation for your system.
If you run the tcsh shell,
ulimit does not work!
tcsh also reports incorrect values when
you ask for the current limits. In this case, you should
start mysqld_safe using
B.1.2.19. Table-Corruption Issues
If you have started mysqld with
--myisam-recover, MySQL automatically checks
and tries to repair MyISAM tables if they
are marked as 'not closed properly' or 'crashed'. If this
happens, MySQL writes an entry in the
hostname.err file 'Warning:
Checking table ...' which is followed by
Warning: Repairing table if the table needs
to be repaired. If you get a lot of these errors, without
mysqld having died unexpectedly just
before, then something is wrong and needs to be investigated
See also , and
B.1.3. Installation-Related IssuesB.1.3.1. Problems Linking to the MySQL Client Library
When you are linking an application program to use the MySQL
client library, you might get undefined reference errors for
symbols that start with mysql_, such as
those shown here:
/tmp/ccFKsdPa.o: In function `main':
/tmp/ccFKsdPa.o(.text+0xb): undefined reference to `mysql_init'
/tmp/ccFKsdPa.o(.text+0x31): undefined reference to `mysql_real_connect'
/tmp/ccFKsdPa.o(.text+0x57): undefined reference to `mysql_real_connect'
/tmp/ccFKsdPa.o(.text+0x69): undefined reference to `mysql_error'
/tmp/ccFKsdPa.o(.text+0x9a): undefined reference to `mysql_close'
You should be able to solve this problem by adding
-Ldir_path -lmysqlclient at the end of your
link command, where dir_path represents the
pathname of the directory where the client library is located.
To determine the correct directory, try this command:
shell& mysql_config --libs
The output from mysql_config might indicate
other libraries that should be specified on the link command
If you get undefined reference errors for
the uncompress or
compress function, add
-lz to the end of your link command and try
If you get undefined reference errors for a
function that should exist on your system, such as
connect, check the manual page for the
function in question to determine which libraries you should
add to the link command.
You might get undefined reference errors
such as the following for functions that don't exist on your
mf_format.o(.text+0x201): undefined reference to `__lxstat'
This usually means that your MySQL client library was compiled
on a system that is not 100% compatible with yours. In this
case, you should download the latest MySQL source distribution
and compile MySQL yourself. See
You might get undefined reference errors at runtime when you
try to execute a MySQL program. If these errors specify
symbols that start with mysql_ or indicate
that the mysqlclient library can't be
found, it means that your system can't find the shared
libmysqlclient.so library. The fix for
this is to tell your system to search for shared libraries
where the library is located. Use whichever of the following
methods is appropriate for your system:
Add the path to the directory where
libmysqlclient.so is located to the
LD_LIBRARY_PATH environment variable.
Add the path to the directory where
libmysqlclient.so is located to the
LD_LIBRARY environment variable.
Copy libmysqlclient.so to some
directory that is searched by your system, such as
/lib, and update the shared library
information by executing ldconfig.
Another way to solve this problem is by linking your program
statically with the -static option, or by
removing the dynamic MySQL libraries before linking your code.
Before trying the second method, you should be sure that no
other programs are using the dynamic libraries.
B.1.3.2. Problems with File Permissions
If you have problems with file permissions, the
UMASK environment variable might be set
incorrectly when mysqld starts. For
example, MySQL might issue the following error message when
you create a table:
ERROR: Can't find file: 'path/with/filename.frm' (Errcode: 13)
The default UMASK value is
0660. You can change this behavior by
starting mysqld_safe as follows:
shell& UMASK=384
# = 600 in octal
shell& export UMASK
shell& mysqld_safe &
By default, MySQL creates database and RAID
directories with an access permission value of
0700. You can modify this behavior by
setting the UMASK_DIR variable. If you set
its value, new directories are created with the combined
UMASK and UMASK_DIR
values. For example, if you want to give group access to all
new directories, you can do this:
shell& UMASK_DIR=504
# = 770 in octal
shell& export UMASK_DIR
shell& mysqld_safe &
In MySQL 3.23.25 and above, MySQL assumes that the value for
UMASK and UMASK_DIR is
in octal if it starts with a zero.
B.1.4. Administration-Related IssuesB.1.4.1. How to Reset the Root Password
If you have never set a root password for
MySQL, the server does not require a password at all for
connecting as root. However, it is
recommended to set a password for each account. See
If you set a root password previously, but
have forgotten what it was, you can set a new password. The
next two sections show procedures for Windows and Unix
systems, respectively.
B.1.4.1.1. Resetting the Root Password on Windows Systems
Use the following procedure for resetting the password for
any MySQL root accounts on Windows:
Log on to your system as Administrator.
Stop the MySQL server if it is running. For a server
that is running as a Windows service, go to the Services
Start Menu -& Control Panel -& Administrative Tools -& Services
Then find the MySQL service in the list, and stop it.
If your server is not running as a service, you may need
to use the Task Manager to force it to stop.
Create a text file and place the following statements in
it. Replace the password with the password that you want
UPDATE mysql.user SET Password=PASSWORD('MyNewPass') WHERE User='root';
FLUSH PRIVILEGES;
The UPDATE and
FLUSH statements each must be written
on a single line. The UPDATE
statement resets the password for all existing
root accounts, and the
FLUSH statement tells the server to
reload the grant tables into memory.
Save the file. For this example, the file will be named
C:\mysql-init.txt.
Open a console window to get to the command prompt:
Start Menu -& Run -& cmd
Start the MySQL server with the special
--init-file option:
C:\& C:\mysql\bin\mysqld-nt --init-file=C:\mysql-init.txt
If you installed MySQL to a location other than
C:\mysql, adjust the command
accordingly.
The server executes the contents of the file named by
the --init-file option at startup,
changing each root account password.
You can also add the --console option
to the command if you want server output to appear in
the console window rather than in a log file.
If you installed MySQL using the MySQL Installation
Wizard, you may need to specify a
--defaults-file option:
C:\& "C:\Program Files\MySQL\MySQL Server 5.0\bin\mysqld-nt.exe"
--defaults-file="C:\Program Files\MySQL\MySQL Server 5.0\my.ini"
--init-file=C:\mysql-init.txt
The appropriate --defaults-file setting
can be found using the Services Manager:
Start Menu -& Control Panel -& Administrative Tools -& Services
Find the MySQL service in the list, right-click on it,
and choose the Properties option. The
Path to executable field contains the
--defaults-file setting.
After the server has started successfully, delete
C:\mysql-init.txt.
Stop the MySQL server, then restart it in normal mode
again. If you run the server as a service, start it from
the Windows Services window. If you start the server
manually, use whatever command you normally use.
You should now be able to connect to MySQL as
root using the new password.
B.1.4.1.2. Resetting the Root Password on Unix SystemsMySQL Enterprise
For expert advice on security-related issues, subscribe to
the MySQL Enterprise Monitor. For more information, see
Use the following procedure for resetting the password for
any MySQL root accounts on Unix. The
instructions assume that you will start the server so that
it runs using the Unix login account that you normally use
for running the server. For example, if you run the server
using the mysql login account, you should
log in as mysql before using the
instructions. (Alternatively, you can log in as
root, but in this case you
must start start
mysqld with the
--user=mysql option. If you start the
server as root without using
--user=mysql, the server may create
root-owned files in the data directory,
such as log files, and these may cause permission-related
problems for future server startups. If that happens, you
will need to either change the ownership of the files to
mysql or remove them.)
Log on to your system as the Unix
mysql user that the
mysqld server runs as.
Locate the .pid file that contains
the server's process ID. The exact location and name of
this file depend on your distribution, hostname, and
configuration. Common locations are
/var/lib/mysql/,
/var/run/mysqld/, and
/usr/local/mysql/data/. Generally,
the filename has an extension of
.pid and begins with either
mysqld or your system's hostname.
You can stop the MySQL server by sending a normal
kill (not kill -9)
to the mysqld process, using the
pathname of the .pid file in the
following command:
shell& kill `cat /mysql-data-directory/host_name.pid`
Note the use of backticks rather than forward quotes
with the cat these cause the
output of cat to be substituted into
the kill command.
Create a text file and place the following statements in
it. Replace the password with the password that you want
UPDATE mysql.user SET Password=PASSWORD('MyNewPass') WHERE User='root';
FLUSH PRIVILEGES;
The UPDATE and
FLUSH statements each must be written
on a single line. The UPDATE
statement resets the password for all existing
root accounts, and the
FLUSH statement tells the server to
reload the grant tables into memory.
Save the file. For this example, the file will be named
/home/me/mysql-init. The file
contains the password, so it should not be saved where
it can be read by other users.
Start the MySQL server with the special
--init-file option:
shell& mysqld_safe --init-file=/home/me/mysql-init &
The server executes the contents of the file named by
the --init-file option at startup,
changing each root account password.
After the server has started successfully, delete
/home/me/mysql-init.
You should now be able to connect to MySQL as
root using the new password.
Alternatively, on any platform, you can set the new password
using the mysql client (but this approach
is less secure):
Stop mysqld and restart it with the
--skip-grant-tables option.
Connect to the mysqld server with
this command:
shell& mysql
Issue the following statements in the
mysql client. Replace the password
with the password that you want to use.
mysql& UPDATE mysql.user SET Password=PASSWORD('MyNewPass')
WHERE User='root';
mysql& FLUSH PRIVILEGES;
You should now be able to connect to MySQL as
root using the new password.
B.1.4.2. What to Do If MySQL Keeps Crashing
Each MySQL version is tested on many platforms before it is
released. This doesn't mean that there are no bugs in MySQL,
but if there are bugs, they should be very few and can be hard
to find. If you have a problem, it always helps if you try to
find out exactly what crashes your system, because you have a
much better chance of getting the problem fixed quickly.
First, you should try to find out whether the problem is that
the mysqld server dies or whether your
problem has to do with your client. You can check how long
your mysqld server has been up by executing
mysqladmin version. If
mysqld has died and restarted, you may find
the reason by looking in the server's error log. See
On some systems, you can find in the error log a stack trace
of where mysqld died that you can resolve
with the resolve_stack_dump program. See
. Note that the variable values
written in the error log may not always be 100% correct.
Many server crashes are caused by corrupted data files or
index files. MySQL updates the files on disk with the
write() system call after every SQL
statement and before the client is notified about the result.
(This is not true if you are running with
--delay-key-write, in which case data files
are written but not index files.) This means that data file
contents are safe even if mysqld crashes,
because the operating system ensures that the unflushed data
is written to disk. You can force MySQL to flush everything to
disk after every SQL statement by starting
mysqld with the --flush
The preceding means that normally you should not get corrupted
tables unless one of the following happens:
The MySQL server or the server host was killed in the
middle of an update.
You have found a bug in mysqld that
caused it to die in the middle of an update.
Some external program is manipulating data files or index
files at the same time as mysqld
without locking the table properly.
You are running many mysqld servers
using the same data directory on a system that doesn't
support good filesystem locks (normally handled by the
lockd lock manager), or you are running
multiple servers with external locking disabled.
You have a crashed data file or index file that contains
very corrupt data that confused mysqld.
You have found a bug in the data storage code. This isn't
likely, but it's at least possible. In this case, you can
try to change the storage engine to another engine by
using ALTER TABLE on a repaired copy of
the table.
Because it is very difficult to know why something is
crashing, first try to check whether things that work for
others crash for you. Please try the following things:
Stop the mysqld server with
mysqladmin shutdown, run
myisamchk --silent --force */*.MYI from
the data directory to check all MyISAM
tables, and restart mysqld. This
ensures that you are running from a clean state. See
Start mysqld with the
--log option and try to determine from
the information written to the log whether some specific
query kills the server. About 95% of all bugs are related
to a particular query. Normally, this is one of the last
queries in the log file just before the server restarts.
See . If you can repeatedly
kill MySQL with a specific query, even when you have
checked all tables just before issuing it, then you have
been able to locate the bug and should submit a bug report
for it. See .
Try to make a test case that we can use to repeat the
problem. See
Try running the tests in the
mysql-test directory and the MySQL
benchmarks. See . They
should test MySQL rather well. You can also add code to
the benchmarks that simulates your application. The
benchmarks can be found in the
sql-bench directory in a source
distribution or, for a binary distribution, in the
sql-bench directory under your MySQL
installation directory.
Try the fork_big.pl script. (It is
located in the tests directory of
source distributions.)
If you configure MySQL for debugging, it is much easier to
gather information about possible errors if something goes
wrong. Configuring MySQL for debugging causes a safe
memory allocator to be included that can find some errors.
It also provides a lot of output about what is happening.
Reconfigure MySQL with the --with-debug
or --with-debug=full option to
configure and then recompile. See
Make sure that you have applied the latest patches for
your operating system.
Use the --skip-external-locking option to
mysqld. On some systems, the
lockd lock manager does not work
the --skip-external-locking
option tells mysqld not to use external
locking. (This means that you cannot run two
mysqld servers on the same data
directory and that you must be careful if you use
myisamchk. Nevertheless, it may be
instructive to try the option as a test.)
Have you tried mysqladmin -u root
processlist when mysqld
appears to be running but not responding? Sometimes
mysqld is not comatose even though you
might think so. The problem may be that all connections
are in use, or there may be some internal lock problem.
mysqladmin -u root processlist usually
is able to make a connection even in these cases, and can
provide useful information about the current number of
connections and their status.
Run the command mysqladmin -i 5 status
or mysqladmin -i 5 -r status in a
separate window to produce statistics while you run your
other queries.
Try the following:
Start mysqld from
gdb (or another debugger). See
Run your test scripts.
Print the backtrace and the local variables at the
three lowest levels. In gdb, you
can do this with t}