|SYSSTAT(5)||Linux User's Manual||SYSSTAT(5)|
sysstat - sysstat configuration file.
This file is read by sa1(8) and sa2(8) shell scripts from the sysstat's set of tools. It consists of a sequence of shell variable assignments used to configure sysstat logging. The variables and their meanings are:
- Number of days after which daily data files are to be compressed. The compression program is given in the ZIP variable.
- Tell sa2 script to wait for a random delay in the indicated range before running. This delay is expressed in seconds, and is aimed at preventing a massive I/O burst at the same time on VM sharing the same storage area. A value of 0 means that sa2 script will generate its reports files immediately.
- The number of days during which a daily data file or a report should be
kept. Data files or reports older than this number of days will be removed
by the sa2(8) shell script. Data files and reports are normally
saved in the /var/log/sa directory, under the name saDD (for data
files) or sarDD (for reports), where the DD parameter
indicates the current day.
The number of files actually kept in the /var/log/sa directory may be slightly higher than the HISTORY value due to the way the sa2 script figures out which files are to be removed (see below "How the sa2(8) script applies HISTORY value"). Using a value of 28 keeps a whole month's worth of data. If you set HISTORY to a value greater than 28 then you should consider using sadc's option -D to prevent older data files from being overwritten (see sadc(8) manual page). In this latter case data files are named saYYYYMMDD and reports sarYYYYMMDD, where YYYY stands for the current year, MM for the current month and DD for the current day.
How the sa2(8) script applies HISTORY value
The sa2 script uses the find command with the -mtime option to figure out which files are to be removed. The find command interprets this value as "N 24 hour periods", ignoring any fractional part. This means that the last modified time of a given sa[r]DD data or report file, using a HISTORY of 1, has to have been modified at least two days ago before it will be removed. And for a HISTORY of 28 that would mean 29 days ago.
To figure out how a HISTORY of 28 is applied in practice, we need to consider that the sa2 script that issues the find command to remove the old files typically runs just before mid-night on a given system, and since the first record from sadc can also be written to the previous day's data file (thereby moving its modification time up a bit), the sa2 script will leave 30 files untouched. So for a setting of 28, and counting the data file of the current day, there will always be 31 files (or 30 files, depending on the number of days in a month) in the /var/log/sa directory during the majority of a given day. E.g.:
April 30th: 31 files (Apr 30th-1st, Mar 31th)
May 1st: 30 files (May 1st, Apr 30th-2nd)
Yet we can note the following exceptions (as inspected at Noon of the given day):
February 28th: 31 files (Feb 28th-1st, Jan 31st, 30th & 29th)
March 1st: 30 files (Mar 1st, Feb 28th-2nd, Jan 31st & 30th)
March 2nd: 29 files (Mar 1st & 2nd, Feb 28th-3rd, Jan. 31st)
March 3rd: 28 files (Mar 1st-3rd, Feb 28th-4th)
March 4th - March 28th: 28 files
March 29th: 29 files
March 30th: 30 files
March 31st: 31 files
(Determining the number of files in March on a leap year is left as an exercise for the reader).
Things are simpler if you use the sa[r]YYYYMMDD name format. Apply the same logic as above in this case and you will find that there are always HISTORY + 3 files in the /var/log/sa directory during the majority of a given day.
- Set this variable to false to prevent the sa2 script from generating reports (the sarDD files).
- Directory where the standard system activity daily data and report files are saved. Its default value is /var/log/sa.
- Options that should be passed to sadc(8). With these options (see sadc(8) manual page), you can select some additional data which are going to be saved in daily data files. These options are used only when a new data file is created. They will be ignored with an already existing one.
- By default sa2 script generates yesterday's summary, since the cron job usually runs right after midnight. If you want sa2 to generate the summary of the same day (for example when cron job runs at 23:53) set this variable to no.
- Program used to compress data and report files.
Sebastien Godard (sysstat <at> orange.fr)