操作系统Linux

Linux-iostat命令详解

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近期在排查生产环境故障时要用到vmstat, iostat, sar, top, tcpdump等命令，以前时不时用到它们，但都没有形成一个完整的文档 ，以致在用到时还需要查一些资料。这篇文章主要说明iostat命令。
iostat命令有两个用途：

  • 输出CPU的统计信息
  • 输出设备和分区的I/O统计信息

环境 | Enviroment

  • RedHat-5.7 64bit

命令语法及参数说明 | Syntax And Paramenter Description

语法：

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iostat [ -c | -d ] [ -k | -m ] [ -t ] [ -V ] [ -x ] [ -n ] [ -h ] [ device [ ... ] | ALL ] [ -p [ device | ALL ] ] [ interval [count ] ]

参数说明：

参数 描述
-c The -c option is exclusive of the -d option and displays only the CPU usage report. 输出CPU统计信息。不能与-d参数同时使用。
-d The -d option is exclusive of the -c option and displays only the device utilization report. 输出设备和分区的I/O统计信息。不能与-c参数同时使用。
-k Display statistics in kilobytes per second instead of blocks per second. Data displayed are valid only with kernels 2.4 and newer. 用“kbytes/秒”代替“块/秒”显示统计信息。在内核2.4以及新版中才有效。
-m Display statistics in megabytes per second instead of blocks or kilobytes per second. Data displayed are valid only with kernels 2.4 and newer. 用“mbytes/秒”代替“块/秒”显示统计信息。在内核2.4以及新版中才有效。
-t Displays the NFS-directory statistic. Data displayed are valid only with kernels 2.6.17 and newer. This option is exclusive ot the -x option. 显示NFS目录统计信息。在内核2.6.17以及新版中才有效。不能与参数-x同时使用。
-V Print version number then exit. 显示版本号并通出。
-x Display extended statistics. This option is exclusive of the -p and -n, and works with post 2.5 kernels since it needs /proc/diskstats file or a mounted sysfs to get the statistics. This option may also work with older kernels (e.g. 2.4) only if extended statistics are available in /proc/partitions (the kernel needs to be patched for that). 显示扩展统计信息。不能与参数-p和-n同时使用，并且需要在内核2.5以上才能使用，因为它需要/proc/diskstats 或者 加载sysfs获取统计信息。如果只是统计/proc/partitios的扩展统计信息，这个参数可能也能在老版本的内核（如：2.4）中工作（需要给内核打补丁）
-n Displays the NFS-directory statistic. Data displayed are valid only with kernels 2.6.17 and newer. This option is exclusive ot the -x option. 显示NFS目录统计信息。需要内核2.6.17或更新版本才有效。不能与参数-x同时使用。
-h Display the NFS report more human readable. 可读性更好的NFS目录统计信息
-p [ { device | ALL } ] The -p option is exclusive of the -x option and displays statistics for block devices and all their partitions that are used by the system. If a device name is entered on the command line, then statistics for it and all its partitions are displayed. Last, the ALL keyword indicates that statistics have to be displayed for all the block devices and partitions defined by the system, including those that have never been used. Note that this option works only with post 2.5 ker-nels. 显示系统使用的块设备和它们的分区统计信息。不能与参数-x同时使用。如果命令中指定了设备名称，显示设备和它的所有分区的统计。如果使用了关键字ALL，将显示系统所有块设备和分区统计信息，即使它们没有被使用。只有在内核2.5或更新版本中有效。
interval 刷新时间间隔
count 刷新次数

CPU统计信息字段说明 | CPU Utilization Report Field Description

参数 描述
%user Show the percentage of CPU utilization that occurred while executing at the user level (application). 用户进程使用的CPU使用率百分比。
%nice Show the percentage of CPU utilization that occurred while executing at the user level with nice priority.
%system Show the percentage of CPU utilization that occurred while executing at the system level (kernel). 系统进程使用的CPU使用率百分比。
%iowait Show the percentage of time that the CPU or CPUs were idle during which the system had an outstanding disk I/O request. 系统输出数据至磁盘时空闲的CPU时间百分比（即IO等待）。
%steal Show the percentage of time spent in involuntary wait by the virtual CPU or CPUs while the hypervisor was servic-ing another virtual processor.
%idle Show the percentage of time that the CPU or CPUs were idle and the system did not have an outstanding disk I/O request. 系统没有任何数据输出至磁盘的CPU时间百分比（即空闲时间）

设备统计信息字段说明 | Device Utilization Report Field Description

参数 描述
Device This column gives the device (or partition) name, which is displayed as hdiskn with 2.2 kernels, for the nth device. It is displayed as devm-n with 2.4 kernels, where m is the major number of the device, and n a distinc-tive number. With newer kernels, the device name as listed in the /dev directory is displayed. 设备或分区名称。
tps Indicate the number of transfers per second that were issued to the device. A transfer is an I/O request to the device. Multiple logical requests can be combined into a single I/O request to the device. A transfer is of inde-terminate size. 设备每秒的传输次数。一个IO请求表示一个传输。多个逻辑请求可以被组成一个I/O请求。一个传输的大小未知。
Blk_read/s Indicate the amount of data read from the device expressed in a number of blocks per second. Blocks are equiva-lent to sectors with 2.4 kernels and newer and therefore have a size of 512 bytes. With older kernels, a block is of indeterminate size. 每秒从设备读取数据量（单位：数据块）。
Blk_wrtn/s Indicate the amount of data written to the device expressed in a number of blocks per second. 每秒写入设备的数据量（单位：数据块）。
Blk_read The total number of blocks read. 读取的总数量（单位：数据块）。
Blk_wrtn The total number of blocks written. 写入的总数量（单位：数据块）。
kB_read/s Indicate the amount of data read from the device expressed in kilobytes per second. 每秒从设备读取的数据量（单位：KB）
kB_wrtn/s Indicate the amount of data written to the device expressed in kilobytes per second. 每秒写入设备的数据量（单位：KB）
kB_read The total number of kilobytes read. 读取的总数量（单位：KB）
kB_wrtn The total number of kilobytes written. 写入的总数量（单位：KB）。
MB_read/s Indicate the amount of data read from the device expressed in megabytes per second. 每秒从设备读取的数据量（单位：MB）
MB_wrtn/s Indicate the amount of data written to the device expressed in megabytes per second. 每秒写入设备的数据量（单位：MB）
MB_read The total number of megabytes read. 读取的总数量（单位：MB）
MB_wrtn The total number of megabytes written. 写入的总数量（单位：MB）。
rrqm/s The number of read requests merged per second that were queued to the device. 每秒被合并的读请求数。
wrqm/s The number of write requests merged per second that were queued to the device. 每秒被合并的写请求数。
r/s The number of read requests that were issued to the device per second. 每秒的读请求数。
w/s The number of write requests that were issued to the device per second. 每秒的写请求数。
rsec/s The number of sectors read from the device per second. 每秒读取的扇区数。
wsec/s The number of sectors written to the device per second. 每秒写入的扇区数。
rkB/s The number of kilobytes read from the device per second. 每秒从设备读取的数据量（单位：KB）
wkB/s The number of kilobytes written to the device per second. 每秒写入设备的数据量（单位：KB）
rMB/s The number of megabytes read from the device per second. 每秒从设备读取的数据量（单位：MB）
wMB/s The number of megabytes written to the device per second. 每秒写入设备的数据量（单位：MB）
avgrq-sz The average size (in sectors) of the requests that were issued to the device.
avgqu-sz The average queue length of the requests that were issued to the device.
await The average time (in milliseconds) for I/O requests issued to the device to be served. This includes the time spent by the requests in queue and the time spent servicing them. I/O请求等待时间的平均值（单位：毫秒）。
svctm The average service time (in milliseconds) for I/O requests that were issued to the device. I/O请求处理时间的平均值（单位：毫秒）。
%util Percentage of CPU time during which I/O requests were issued to the device (bandwidth utilization for the device). Device saturation occurs when this value is close to 100%. 消耗在I/O请求中的CPU时间百分比（设备带宽利用率）。如果该值接近100%说明设备出现了瓶颈。

示例 | Examples

1、统计CPU使用情况

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iostat -c 1 3

输出信息如下：

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Linux 2.6.18-274.3.1.el5 (nieyong-redhat)       2013年04月13日
avg-cpu:  %user   %nice %system %iowait  %steal   %idle
           0.39    0.22    0.92    2.80    0.00   95.68
avg-cpu:  %user   %nice %system %iowait  %steal   %idle
           0.00    0.00    0.00    1.00    0.00   99.00
avg-cpu:  %user   %nice %system %iowait  %steal   %idle
           0.00    0.00    0.00    0.00    0.00  100.00

2、统计磁盘使用情况

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iostat -d 1 3

输出信息如下：

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Linux 2.6.18-274.3.1.el5 (nieyong-redhat)       2013年04月13日
Device:            tps   Blk_read/s   Blk_wrtn/s   Blk_read   Blk_wrtn
sda               6.39       124.29        27.41    1418077     312756
sda1              0.01         0.16         0.00       1826          4
sda2              6.38       123.95        27.41    1414210     312752
sda3              0.01         0.14         0.00       1617          0
hda               0.00         0.01         0.00        152          0
Device:            tps   Blk_read/s   Blk_wrtn/s   Blk_read   Blk_wrtn
sda               0.00         0.00         0.00          0          0
sda1              0.00         0.00         0.00          0          0
sda2              0.00         0.00         0.00          0          0
sda3              0.00         0.00         0.00          0          0
hda               0.00         0.00         0.00          0          0
Device:            tps   Blk_read/s   Blk_wrtn/s   Blk_read   Blk_wrtn
sda               0.00         0.00         0.00          0          0
sda1              0.00         0.00         0.00          0          0
sda2              0.00         0.00         0.00          0          0
sda3              0.00         0.00         0.00          0          0
hda               0.00         0.00         0.00          0          0

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