ServerBuddies Support Blog

Growing a File System on a Logical Volume

To grow a file system on a logical volume, perform the following steps:

1. Make a new physical volume.
2. Extend the volume group that contains the logical volume with the file system you are growing to include the new physical volume.
3. Extend the logical volume to include the new physical volume.
4. Grow the file system.

*If you have sufficient unallocated space in the volume group, you can use that space to extend the logical volume instead of performing steps 1 and 2.

MX priority

The relative priority of an MX server is strong-minded by the preference number present in the DNS MX record. When a remote client does an MX lookup for the domain name, it gets a list of servers and their first choice numbers. The MX record with the smallest first choice number has the highest precedence and is the first server to be tried. The remote client will go down the list of servers until it successfully delivers the message or gets permanently rejected due to an inaccessible server or if the mail account does not exist on that server. If there is more than one entry with the same preference number, all of those must be tried before moving on to lower-priority entries.

strace - trace system calls and signals

In the simplest case strace runs the specified command until it exits.

It intercepts and records the system calls which are called by a process and the signals which are received by a process. The name of each system call, its arguments and its return value are printed on standard error or to the file specified with the -o option.

strace is a useful diagnostic, instructional, and debugging tool. System administrators, diagnosticians and trouble-shooters will find it invaluable for solving problems with programs for which the source is not readily available since they do not need to be recompiled in order to trace them. Students, hackers and the overly-curious will find that a great deal can be learned about a system and its system calls by tracing even ordinary programs.

And pro?grammers will find that since system calls and signals are events that happen at the user/kernel interface, a close examination of this boundary is very useful for bug isolation, sanity checking and attempting to capture race conditions.

Example:

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sar - Collect, report, or save system activity information.

To have sar read a particular data file, use the -f /var/log/sa/saDD option. You can select multiple files by using multiple -f options. Since many of sar’s reports are lengthy, you may want to pipe the output to a file.

To create a basic report showing CPU usage and I/O wait time percentage, use sar with no flags. It produces a report similar to this:

“The %user and %system columns simply specify the amount of time the CPU spends in user and system mode. The %iowait and %idle columns are of interest to us when doing performance analysis. The %iowait column specifies the amount of time the CPU spends waiting for I/O requests to complete. The %idle column tells us how much useful work the CPU is doing. A %idle time near zero indicates a CPU bottleneck, while a high %iowait value indicates unsatisfactory disk performance.”