Section (2) acct

Linux manual pages Section 2  


acct — switch process accounting on or off


#include <unistd.h>
int acct( const char *filename);
[Note] Note
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
Since glibc 2.21:
_DEFAULT_SOURCE In glibc 2.19 and 2.20:
_DEFAULT_SOURCE || (_XOPEN_SOURCE && _XOPEN_SOURCE < 500) Up to and including glibc 2.19:


The acct() system call enables or disables process accounting. If called with the name of an existing file as its argument, accounting is turned on, and records for each terminating process are appended to filename as it terminates. An argument of NULL causes accounting to be turned off.


On success, zero is returned. On error, −1 is returned, and errno is set appropriately.



Write permission is denied for the specified file, or search permission is denied for one of the directories in the path prefix of filename (see also path_resolution(7)), or filename is not a regular file.


filename points outside your accessible address space.


Error writing to the file filename.


filename is a directory.


Too many symbolic links were encountered in resolving filename.


filename was too long.


The system-wide limit on the total number of open files has been reached.


The specified file does not exist.


Out of memory.


BSD process accounting has not been enabled when the operating system kernel was compiled. The kernel configuration parameter controlling this feature is CONFIG_BSD_PROCESS_ACCT.


A component used as a directory in filename is not in fact a directory.


The calling process has insufficient privilege to enable process accounting. On Linux, the CAP_SYS_PACCT capability is required.


filename refers to a file on a read-only filesystem.


There are no more free file structures or we ran out of memory.


SVr4, 4.3BSD (but not POSIX).


No accounting is produced for programs running when a system crash occurs. In particular, nonterminating processes are never accounted for.

The structure of the records written to the accounting file is described in acct(5).




This page is part of release 4.16 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at−pages/.

  Copyright (c) 1993 Michael Haardt
Fri Apr  2 11:32:09 MET DST 1993

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Modified 1993-07-22 by Rik Faith <>
Modified 1993-08-10 by Alan Cox <>
Modified 1998-11-04 by Tigran Aivazian <>
Modified 2004-05-27, 2004-06-17, 2004-06-23 by Michael Kerrisk

Section (5) acct

Linux manual pages Section 5  


acct — process accounting file


#include <sys/acct.h>


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


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 kernel 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 */


The acct_v3 structure is defined in glibc since version 2.6.


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


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

In kernels up to and including 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.


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


This page is part of release 4.16 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at−pages/.

  Copyright (C) 2008, Michael Kerrisk <>

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