使用fpdf读取PDF文件时，报错：This PDF document probably uses a compression technique which is not supported by the free parser shipped with FPDI. (See https://www.setasign.com/fpdi-pdf-parser for more details)
docker system prune命令可以用于清理磁盘，删除关闭的容器、无用的数据卷和网络，以及dangling镜像(即无tag的镜像)。docker system prune -a命令清理得更加彻底，可以将没有容器使用Docker镜像都删掉。注意，这两个命令会把你暂时关闭的容器，以及暂时没有用到的Docker镜像都删掉了…所以使用之前一定要想清楚吶。
执行docker system prune -a命令之后，Docker占用的磁盘空间减少了很多：
docker system df TYPE TOTAL ACTIVE SIZE RECLAIMABLE Images 10 10 2.271GB 630.7MB (27%) Containers 10 10 2.211MB 0B (0%) Local Volumes 3 3 1.421GB 0B (0%) Build Cache 0B 0B
docker ps CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES a376aa694b22 192.168.59.224:5000/nginx:1.12.1 "nginx -g 'daemon off" 9 weeks ago Up 10 minutes nginx
还有一次，当我清理了镜像、容器以及数据卷之后，发现磁盘空间并没有减少。根据Docker disk usage提到过的建议，我重启了Docker，发现磁盘使用率从83%降到了19%。根据高手指点，这应该是与内核3.13相关的BUG，导致Docker无法清理一些无用目录：
it’s quite likely that for some reason when those container shutdown, docker couldn’t remove the directory because the shm device was busy. This tends to happen often on 3.13 kernel. You may want to update it to the 4.4 version supported on trusty 14.04.5 LTS.
The reason it disappeared after a restart, is that daemon probably tried and succeeded to clean up left over data from stopped containers.
再比如2538错误：Connx CompCode:2 Reason:2538 Text:An MQCONN call was issued from a client to connect to a queue manager but the attempt to allocate a conversation to the remote system failed
这2538就是TMD连接不上服务器，后来问了对方，原来，对方挂了。我晕
今天又是2538，再一问，我靠，换IP了。。真受不了
然后改好IP，再连接，结果。。。2539出现了：Reason:2539 Text:An MQCONN call was issued from a client to connect to a queue manager but the attempt to establish communication failed
查了下2539对应的错误：
XML/HTML代码
2539 (09EB) (RC2539): MQRC_CHANNEL_CONFIG_ERROR
Explanation
An MQCONN call was issued from a client to connect to a queue manager but the attempt to establish communication failed. Common causes of this reason code are:
a.The server and client cannot agree on the channel attributes to use.
b.There are errors in one or both of the QM.INI or MQCLIENT.INI configuration files.
c.The server machine does not support the code page used by the client.
A CCSID is a Coded Character Set Identifier. The Unicode standard defines a Coded Character Set as "A character set in which each character is assigned a numeric code value." This means that a CCSID is a number that defines a numeric ordering of characters. The IBM ® Character Data Representation Architecture (CDRA) as defined in SC09-1390, defines CCSIDs that are used with IBM to represent character data. This architecture defines Single Byte Character Set (SBCS) CCSIDs, Multiple Byte Character Set (MBCS) CCSIDs, and Mixed CCSIDs which are a combination of SBCS and MBCS data. MBCS CCSIDs are usually used for languages, such as Chinese, Japanese, and Korean, that define a larger number of characters than can be represented in a single byte.
All SBCS CCSIDs define a similar basic set of characters, although they might define them in different numeric ordering. For instance all SBCS EBCDIC CCSIDs define the number "1" as x'F0' and all SBCS ASCII CCSIDs define the number 1 as x'30'.
