sar gets its info from /proc/loadavg (on Linux OSs), just like top and uptime do...

Erwin · on April 6, 2010

We must be running different versions of sar then, as "sar" by itself here (RHEL 5) shows information about the time split between user/system/waitIO/idle -- that certainly does not come from /proc/loadavg.

If you run "sar -q" you could get the load average information, but that's not particularly useful, as you can't see whether the 20 load avg an hour ago was caused by heavy disk IO or a dozen CPU bound processes.

nailer · on April 6, 2010

Nope, we're likely running the same version. The particular info you mentioned comes from /proc/stat (you're right that it's a different file), but again it's the same sources as top:

    # lsb_release -d
    Description:    Red Hat Enterprise Linux Server release 5.3 (Tikanga)

    # rpm -qf $(which sar)
    sysstat-7.0.2-3.el5

    # strace /usr/lib64/sa/sa1 1 1 &> results

    # grep open results                      
    open("/etc/ld.so.cache", O_RDONLY)      = 3
    open("/lib64/libtermcap.so.2", O_RDONLY) = 3
    open("/lib64/libdl.so.2", O_RDONLY)     = 3
    open("/lib64/libc.so.6", O_RDONLY)      = 3
    open("/dev/tty", O_RDWR|O_NONBLOCK)     = 3
    open("/proc/meminfo", O_RDONLY)         = 3
    open("/usr/lib64/sa/sa1", O_RDONLY)     = 3
    open("/etc/ld.so.cache", O_RDONLY)      = 3
    open("/lib64/libc.so.6", O_RDONLY)      = 3
    open("/etc/localtime", O_RDONLY)        = 3
    open("/sys/devices/system/cpu", O_RDONLY|O_NONBLOCK|O_DIRECTORY) = 3
    open("/proc/tty/driver/serial", O_RDONLY) = 3
    open("/proc/interrupts", O_RDONLY)      = 3
    open("/proc/net/dev", O_RDONLY)         = 3
    open("/proc/diskstats", O_RDONLY)       = 3
    open("/var/log/sa/sa06", O_RDWR|O_APPEND) = 3
    open("/proc/stat", O_RDONLY)            = 4
    open("/proc/meminfo", O_RDONLY)         = 4
    open("/proc/loadavg", O_RDONLY)         = 4
    open("/proc/vmstat", O_RDONLY)          = 4
    open("/proc/sys/fs/dentry-state", O_RDONLY) = 4
    open("/proc/sys/fs/file-nr", O_RDONLY)  = 4
    open("/proc/sys/fs/inode-state", O_RDONLY) = 4
    open("/proc/sys/fs/super-max", O_RDONLY) = -1 ENOENT (No such file or directory)
    open("/proc/sys/fs/dquot-max", O_RDONLY) = -1 ENOENT (No such file or directory)
    open("/proc/sys/kernel/rtsig-max", O_RDONLY) = -1 ENOENT (No such file or directory)
    open("/proc/net/sockstat", O_RDONLY)    = 4
    open("/proc/net/rpc/nfs", O_RDONLY)     = -1 ENOENT (No such file or directory)
    open("/proc/net/rpc/nfsd", O_RDONLY)    = -1 ENOENT (No such file or directory)
    open("/proc/diskstats", O_RDONLY)       = 4
    open("/proc/tty/driver/serial", O_RDONLY) = 4
    open("/proc/interrupts", O_RDONLY)      = 4
    open("/proc/net/dev", O_RDONLY)         = 4

    # strace top -n -b 1 &> results
    # grep open results 
    open("/etc/ld.so.cache", O_RDONLY)      = 3
    open("/lib64/libproc-3.2.7.so", O_RDONLY) = 3
    open("/usr/lib64/libncurses.so.5", O_RDONLY) = 3
    open("/lib64/libc.so.6", O_RDONLY)      = 3
    open("/lib64/libdl.so.2", O_RDONLY)     = 3
    open("/proc/stat", O_RDONLY)            = 3
    open("/proc/sys/kernel/pid_max", O_RDONLY) = 3
    open("/etc/toprc", O_RDONLY)            = -1 ENOENT (No such file or directory)
    open("/root/.toprc", O_RDONLY)          = -1 ENOENT (No such file or directory)