Category Archives: Performance
netstat is a command line utility in Unix, Linux and Unix like systems to show information about
- network connections,
- routing tables,
- interface statistics,
- mas-querade connections
- multicast memberships
By default, netstat displays a list of open sockets of all configured address families , tcp , udp etc.
netstat provide very extensive network details and here are the top netstat usage with different options to get you the just the information you need.
Application monitoring is a very important aspect of a project but unfortunately not much attention is paid to develop the effective monitoring while the projects are still movingh to completions. Once project is complete & live lack of proper monitoring costs in terms of downtime when support persons are not aware if application is having some problems or application not working at all.
fsck, similar to chkdsk in windows, checks and repairs the file system in Unix & Linux operating systems. Learn about fsck modes, phases & fsck errors messages
fsck, File System Consistency checK, is a system utility in Unix, Linux and other Unix like systems for checking and repairing file system inconsistencies.
File system can become inconsistent due to several reasons and the most common is abnormal shutdown due to hardware failure, power failure or switching off the system without proper shutdown. Due to these reasons the superblock in a file system is not updated and has mismatched information relating to system data blocks, free blocks and inodes.
fsck in Linux
fsck in this document is refered with reference to ufs file system but it can be used in Linux systems as
fsck -t ext2 /dev/sda3
it returns with any of the followig code
0 – No errors
1 – File system errors corrected
2 – System should be rebooted
4 – File system errors left uncorrected
8 – Operational error
16 – Usage or syntax error
32 – Fsck canceled by user request
128 – Shared library error
fsck checks the file systems defined in /etc/fstab in Linux and /etc/vfstab in Unix systems
This document is primarily written with reference to Solaris performance monitoring and tuning but these tools are available in other Unix variants & Linux also with slight syntax difference.
iostat , vmstat and netstat are three most commonly used tools for performance monitoring . These comes built in with the operating system and are easy to use .iostat stands for input output statistics and reports statistics for i/o devices such as disk drives . vmstat gives the statistics for virtual Memory and netstat gives the network statistics .
Following pages describes these tools and their usage for performance monitoring explains their syntax , examples and explanantion of results and solution for the common problems.
iostat – Input Output statistics
iostat reports terminal and disk I/O activity and CPU utilization. The first line of output is for the time period since boot & each subsequent line is for the prior interval . Kernel maintains a number of counters to keep track of the values.
iostat’s activity class options default to tdc (terminal, disk, and CPU). If any other option/s are specified, this default is completely overridden i.e. iostat -d will report only statistics about the disks.
Basic synctax is iostat interval count
option – let you specify the device for which information is needed like disk , cpu or terminal. (-d , -c , -t or -tdc ) . x options gives the extended statistics .
interval – is time period in seconds between two samples . iostat 4 will give data at each 4 seconds interval.
count – is the number of times the data is needed . iostat 4 5 will give data at 4 seconds interval 5 times
$ iostat -xtc 5 2 extended disk statistics tty cpu disk r/s w/s Kr/s Kw/s wait actv svc_t %w %b tin tout us sy wt id sd0 2.6 3.0 20.7 22.7 0.1 0.2 59.2 6 19 0 84 3 85 11 0 sd1 4.2 1.0 33.5 8.0 0.0 0.2 47.2 2 23 sd2 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0 0 sd3 10.2 1.6 51.4 12.8 0.1 0.3 31.2 3 31 The fields have the following meanings: disk name of the disk r/s reads per second w/s writes per second Kr/s kilobytes read per second Kw/s kilobytes written per second wait average number of transactions waiting for service (Q length) actv average number of transactions actively being serviced (removed from the queue but not yet completed) %w percent of time there are transactions waiting for service (queue non-empty) %b percent of time the disk is busy (transactions in progress)
iostat Results and Solutions
The values to look from the iostat output are:
* Reads/writes per second (r/s , w/s)
* Percentage busy (%b)
* Service time (svc_t)
If a disk shows consistently high reads/writes along with , the percentage busy (%b) of the disks is greater than 5 percent, and the average service time (svc_t) is greater than 30 milliseconds, then one of the following action needs to be taken
- Tune the application to use disk i/o more efficiently by modifying the disk queries and using available cache facilities of application servers .
- Spread the file system of the disk on to two or more disk using disk striping feature of volume manager /disksuite etc.
- Increase the system parameter values for inode cache , ufs_ninode , which is Number of inodes to be held in memory. Inodes are cached globally (for UFS), not on a per-file system basis
- Move the file system to another faster disk /controller or replace existing disk/controller to a faster one.