NAME

       acct - process accounting file

SYNOPSIS

       #include <sys/acct.h>

DESCRIPTION

       If the kernel is built with the process accounting option enabled (CONFIG_BSD_PROCESS_ACCT), then calling
       acct(2) starts process accounting, for example:

           acct("/var/log/pacct");

       When process accounting is enabled, the kernel writes a record to the accounting file as each process  on
       the  system terminates.  This record contains information about the terminated process, and is defined in
       <sys/acct.h> as follows:

           #define ACCT_COMM 16

           typedef u_int16_t comp_t;

           struct acct {
               char ac_flag;           /* Accounting flags */
               u_int16_t ac_uid;       /* Accounting user ID */
               u_int16_t ac_gid;       /* Accounting group ID */
               u_int16_t ac_tty;       /* Controlling terminal */
               u_int32_t ac_btime;     /* Process creation time
                                          (seconds since the Epoch) */
               comp_t    ac_utime;     /* User CPU time */
               comp_t    ac_stime;     /* System CPU time */
               comp_t    ac_etime;     /* Elapsed time */
               comp_t    ac_mem;       /* Average memory usage (kB) */
               comp_t    ac_io;        /* Characters transferred (unused) */
               comp_t    ac_rw;        /* Blocks read or written (unused) */
               comp_t    ac_minflt;    /* Minor page faults */
               comp_t    ac_majflt;    /* Major page faults */
               comp_t    ac_swaps;     /* Number of swaps (unused) */
               u_int32_t ac_exitcode;  /* Process termination status
                                          (see wait(2)) */
               char      ac_comm[ACCT_COMM+1];
                                       /* Command name (basename of last
                                          executed command; null-terminated) */
               char      ac_pad[X];    /* padding bytes */
           };

           enum {          /* Bits that may be set in ac_flag field */
               AFORK = 0x01,           /* Has executed fork, but no exec */
               ASU   = 0x02,           /* Used superuser privileges */
               ACORE = 0x08,           /* Dumped core */
               AXSIG = 0x10            /* Killed by a signal */
           };

       The comp_t data type is a floating-point value consisting of a  3-bit,  base-8  exponent,  and  a  13-bit
       mantissa.  A value, c, of this type can be converted to a (long) integer as follows:

           v = (c & 0x1fff) << (((c >> 13) & 0x7) * 3);

       The  ac_utime,  ac_stime,  and  ac_etime  fields  measure  time  in "clock ticks"; divide these values by
       sysconf(_SC_CLK_TCK) to convert them to seconds.

   Version 3 accounting file format
       Since Linux 2.6.8, an optional alternative version  of  the  accounting  file  can  be  produced  if  the
       CONFIG_BSD_PROCESS_ACCT_V3  option is set when building the kernel.  With this option is set, the records
       written to the accounting file contain additional fields, and the width of c_uid  and  ac_gid  fields  is
       widened from 16 to 32 bits (in line with the increased size of UID and GIDs in Linux 2.4 and later).  The
       records are defined as follows:

           struct acct_v3 {
               char      ac_flag;      /* Flags */
               char      ac_version;   /* Always set to ACCT_VERSION (3) */
               u_int16_t ac_tty;       /* Controlling terminal */
               u_int32_t ac_exitcode;  /* Process termination status */
               u_int32_t ac_uid;       /* Real user ID */
               u_int32_t ac_gid;       /* Real group ID */
               u_int32_t ac_pid;       /* Process ID */
               u_int32_t ac_ppid;      /* Parent process ID */
               u_int32_t ac_btime;     /* Process creation time */
               float     ac_etime;     /* Elapsed time */
               comp_t    ac_utime;     /* User CPU time */
               comp_t    ac_stime;     /* System time */
               comp_t    ac_mem;       /* Average memory usage (kB) */
               comp_t    ac_io;        /* Characters transferred (unused) */
               comp_t    ac_rw;        /* Blocks read or written
                                          (unused) */
               comp_t    ac_minflt;    /* Minor page faults */
               comp_t    ac_majflt;    /* Major page faults */
               comp_t    ac_swaps;     /* Number of swaps (unused) */
               char      ac_comm[ACCT_COMM]; /* Command name */
           };

VERSIONS

       Although it is present on most systems, it is not standardized, and the  details  vary  somewhat  between
       systems.

STANDARDS

       None.

HISTORY

       glibc 2.6.

       Process accounting originated on BSD.

NOTES

       Records in the accounting file are ordered by termination time of the process.

       Up  to  and  including Linux 2.6.9, a separate accounting record is written for each thread created using
       the NPTL threading library; since Linux 2.6.10, a single accounting record  is  written  for  the  entire
       process on termination of the last thread in the process.

       The  /proc/sys/kernel/acct  file,  described  in  proc(5),  defines settings that control the behavior of
       process accounting when disk space runs low.

SEE ALSO

       lastcomm(1), acct(2), accton(8), sa(8)