man > acct(5)

acct(5)                                  File Formats Manual                                 acct(5)

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  val‐
       ues 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 cre‐
       ated 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 be‐
       havior of process accounting when disk space runs low.

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

Linux man-pages 6.7                          2023-10-31                                      acct(5)