View source for Strace

{{short description|Diagnostic, debugging and instructional userspace utility for Linux}}
{{Lowercase|strace}}
{{Infobox software
|name                    = strace
|logo                    = Strace_logo.svg
|screenshot              =
|caption                 =
|collapsible             =4
|author                  = Paul Kranenburg
|developer               = Dmitry Levin
|released                =
|discontinued            =
| latest release version = {{wikidata|property|preferred|references|edit|P348|P548=Q2804309}}
| latest release date    = {{Start date and age|{{wikidata|qualifier|preferred|single|P348|P548=Q2804309|P577}}|df=yes}}
|latest preview version  =
|latest preview date     =
|programming language    = [[C (programming language)|C]]<ref>{{cite web|url=https://openhub.net/p/strace |title=The strace Open Source Project on Open Hub |publisher=Openhub.net |date= |accessdate=2021-11-23}}</ref>
|operating system        = [[Linux]]
|platform                = [[AArch64]], [[DEC Alpha]], [[ARC (processor)|ARC]], [[ARM architecture|ARM EABI/OABI]], [[AVR32]], [[Blackfin]], C-SKY, [[PA-RISC|HP PA-RISC]], [[IA-32]], [[IA-64]], [[LoongArch]], [[Motorola 68000 series|Motorola 68k]], [[Imagination META]], [[MicroBlaze]], [[MIPS architecture|MIPS]], [[Nios II]], [[OpenRISC]], [[Power ISA]] 32/64 bit, [[RISC-V]], [[System/390]]/[[z/Architecture]], [[SuperH]] 32/64 bit, [[SPARC]] 32/64 bit, [[TILE64|TILE]], [[TILEPro64|TILEPro]], [[TILE-Gx]], [[x86-64]], [[x32 ABI]], [[Xtensa]]
|size                    =
|language                = [[English language|English]]{{refn|group=note|Decoding of system error messages, however, is performed in accordance with the current locale since strace 4.22.<ref>{{cite mailing list
 | url = https://lists.strace.io/pipermail/strace-devel/2018-April/008103.html
 | title = [PATCH] Add i18n support
 | author = Dmitry V. Levin
 | date = 2018-04-01
 | accessdate= 2021-09-02
}}</ref>}}
|genre                   = [[Debugging]]
|license                 = [[GNU Lesser General Public License|LGPL v2.1+]]<ref group="note">The test suite is licensed under [[GNU General Public License|GPL v2.0+]].</ref><ref>{{cite mailing list
 | url = https://lists.strace.io/pipermail/strace-devel/2018-December/008548.html
 | title = I: changing the license of strace to a copyleft license
 | author = Dmitry V. Levin
 | date = 2018-12-15
 | accessdate= 2021-09-02
}}</ref>
}}

'''strace''' is a diagnostic, [[debugging]] and instructional [[userspace]] utility for [[Linux]].  It is used to monitor and tamper with interactions between [[Process (computing)|processes]] and the [[Linux kernel]], which include [[system call]]s, [[Unix signal|signal]] deliveries, and changes of process state.  The operation of strace is made possible by the kernel feature known as [[ptrace]].

Some [[Unix-like]] systems provide other diagnostic tools similar to strace, such as truss.

== History ==
Strace was originally written for [[SunOS]] by Paul Kranenburg in 1991, according to its copyright notice, and published early in 1992, in volume three of comp.sources.sun.  The initial [[README]] file contained the following:<ref>{{cite newsgroup |url=https://stuff.mit.edu/afs/sipb/project/eichin/cruft/machine/sun/sun-Strace |author=Paul Kranenburg |date=March 2, 1992 |title=Strace - an alternative syscall tracer |newsgroup=comp.sources.sun}}</ref>

<blockquote>
{{Mono|strace(1)}} is a system call tracer for Sun(tm) systems much like the Sun supplied program {{Mono|trace(1)}}. {{Mono|strace(1)}} is a useful utility to sort of debug programs for which no source is available which unfortunately includes almost all of the Sun supplied system software.
</blockquote>

Later, Branko Lankester ported this version to [[Linux]], releasing his version in November 1992 with the second release following in 1993.<ref>{{cite web |url=http://ftp.funet.fi/pub/Linux/tools/strace.tar.Z |title=first Linux release of strace |author=Branko Lankester |date=November 5, 1992 }}</ref><ref>{{cite web |url=http://ftp.funet.fi/pub/Linux/tools/strace-2.tgz |title=second Linux release of strace |author=Branko Lankester |date=June 18, 1993 }}</ref>  Richard Sladkey combined these separate versions of strace in 1993, and ported the program to [[SVR4]] and [[Solaris (operating system)|Solaris]] in 1994,<ref>{{cite web |url=http://manned.org/strace/e47b83b9 |title=strace |publisher=manned.org |date=June 21, 1994 }}</ref> resulting in strace&nbsp;3.0 that was announced in comp.sources.misc in mid-1994.<ref>{{cite web |url=http://ftp.sunet.se/pub/usenet/ftp.uu.net/comp.sources.misc/index |title=SUNET's Index of /pub/usenet/ftp.uu.net/comp.sources.misc/volume43/strace |accessdate=January 14, 2015 |archive-date=September 11, 2007 |archive-url=https://web.archive.org/web/20070911180544/http://ftp.sunet.se/pub/usenet/ftp.uu.net/comp.sources.misc/index |url-status=dead }}</ref>

Beginning in 1996, strace was maintained by Wichert Akkerman. During his tenure, strace development migrated to [[Concurrent Versions System|CVS]]; ports to [[FreeBSD]] and many architectures on Linux (including ARM, IA-64, MIPS, PA-RISC, PowerPC, s390, SPARC) were introduced. In 2002, the burden of strace maintainership was transferred to Roland McGrath. Since then, strace gained support for several new Linux architectures (AMD64, s390x, SuperH), bi-architecture support for some of them, and received numerous additions and improvements in syscalls decoders on Linux; strace development migrated to [[git]] during that period. Since 2009, strace is actively maintained by Dmitry Levin. strace gained support for AArch64, ARC, AVR32, Blackfin, Meta, Nios II, OpenSISC 1000, RISC-V, Tile/TileGx, Xtensa architectures since that time.

The last version of strace that had some (evidently dead)<ref>{{cite web |url=http://sourceforge.net/p/strace/mailman/message/28799000/ |title=How about removing non-Linux code? |author=Denys Vlasenko |date=February 7, 2012}}</ref> code for non-[[Linux]] operating systems was 4.6, released in March 2011.<ref>{{cite web |url=http://sourceforge.net/p/strace/mailman/message/27209257/ |title=strace 4.6 released |author=Dmitry V. Levin |date=March 16, 2011}}</ref>  In strace version 4.7, released in May 2012,<ref>{{cite web |url=http://sourceforge.net/p/strace/mailman/message/29210530/ |title=strace 4.7 released |author=Dmitry V. Levin |date=May 2, 2012}}</ref> all non-Linux code had been removed;<ref>{{cite web |url=http://sourceforge.net/p/strace/code/ci/v4.7/tree/NEWS |title=Noteworthy changes in release 4.7 |author=Dmitry V. Levin |date=April 20, 2012}}</ref> since strace 4.13,<ref>{{cite web |url=https://lists.strace.io/pipermail/strace-devel/2016-October/005679.html|title=strace 4.14 released|author=Dmitry V. Levin |date=October 4, 2016}}</ref> the project follows Linux kernel's release schedule, and as of version 5.0,<ref>{{cite web |url=https://lists.strace.io/pipermail/strace-devel/2019-March/008672.html|title=strace 5.0 released|author=Dmitry V. Levin |date=March 19, 2019}}</ref> it follows Linux's versioning scheme as well.

In 2012 strace also gained support for path tracing and file descriptor path decoding.<ref>{{cite web|url=https://github.com/strace/strace/blob/v4.7/NEWS|title=Noteworthy changes in release 4.7|author=Dmitry V. Levin|website=[[GitHub]]|date=May 1, 2012}}</ref> In August 2014, strace 4.9 was released,<ref>{{cite web|url=https://lists.strace.io/pipermail/strace-devel/2014-August/003500.html|title=strace 4.9 released|author=Dmitry V. Levin |date=August 15, 2014}}</ref><ref>{{cite web|url=https://github.com/strace/strace/blob/v4.9/NEWS|title=Noteworthy changes in release 4.9|author=Dmitry V. Levin|website=[[GitHub]]|date=August 15, 2014}}</ref> where support for stack traces printing was added. In December 2016,<ref>{{cite web|url=https://lists.strace.io/pipermail/strace-devel/2016-December/005841.html|title=strace 4.15 released|author=Dmitry V. Levin|date=December 14, 2016}}</ref><ref>{{cite web|url=https://github.com/strace/strace/blob/v4.15/NEWS|title=Noteworthy changes in release 4.15|author=Dmitry V. Levin|website=[[GitHub]]|date=December 14, 2016}}</ref> syscall [[fault injection]] feature was implemented.

=== Version history ===
{| class="wikitable mw-collapsible mw-collapsed"
 ! Version
 ! Release date
 ! Notable changes
 |-
 | 6.2 || {{dts|format=dmy|2023|02|26}}<ref>{{cite web|url=https://lists.strace.io/pipermail/strace-devel/2023-February/011172.html|title=strace 6.2 released|author=Dmitry V. Levin|date=2023-02-26}}</ref>
 | Implemented collision resolution for overlapping terminal/sound ioctl commands
 |-
 | 6.1 || {{dts|format=dmy|2022|12|12}}<ref>{{cite web|url=https://lists.strace.io/pipermail/strace-devel/2022-December/011128.html|title=strace 6.1 released|author=Dmitry V. Levin|date=2022-12-12}}</ref>
 | Enhanced decoding of <code>statx</code> syscall and terminal ioctl commands
 |-
 | 6.0 || {{dts|format=dmy|2022|10|29}}<ref>{{cite web|url=https://lists.strace.io/pipermail/strace-devel/2022-October/011125.html|title=strace 6.0 released|author=Dmitry V. Levin|date=2022-10-29}}</ref>
 | Enhanced decoding of <code>setns</code> syscall and <code>PTP_*</code> ioctl commands
 |-
 | 5.19 || {{dts|format=dmy|2022|08|12}}<ref>{{cite web|url=https://lists.strace.io/pipermail/strace-devel/2022-August/011094.html|title=strace 5.19 released|author=Dmitry V. Levin|date=2022-08-12}}</ref>
 | The "(deleted)" marker of unlinked file descriptor paths is no longer interpreted as a part of a path;  enhanced decoding of <code>arch_prctl</code>, <code>io_uring_register</code>, and <code>prctl</code> syscalls; enhanced decoding of <code>siginfo_t</code> structure
 |-
 | 5.18 || {{dts|format=dmy|2022|06|18}}<ref>{{cite web|url=https://lists.strace.io/pipermail/strace-devel/2022-June/011079.html|title=strace 5.18 released|author=Dmitry V. Levin|date=2022-06-18}}</ref>
 | 
 |-
 | 5.17 || {{dts|format=dmy|2022|03|26}}<ref>{{cite web|url=https://lists.strace.io/pipermail/strace-devel/2022-March/011048.html|title=strace 5.17 released|author=Dmitry V. Levin|date=2022-03-27}}</ref>
 | Added support for a new <code>set_mempolicy_home_node</code> syscall on Linux
 |-
 | 5.16 || {{dts|format=dmy|2022|01|10}}<ref>{{cite web|url=https://lists.strace.io/pipermail/strace-devel/2022-January/010884.html|title=strace 5.16 released|author=Dmitry V. Levin|date=2022-01-10}}</ref>
 | Added support for printing SELinux context mismatches (<code>--secontext=mismatch</code> option); added support for a new <code>futex_waitv</code> syscall on Linux
 |-
 | 5.15 || {{dts|format=dmy|2021|12|01}}<ref>{{cite web|url=https://lists.strace.io/pipermail/strace-devel/2021-December/010783.html|title=strace 5.15 released|author=Dmitry V. Levin|date=2021-12-01}}</ref>
 | 
 |-
 | 5.14 || {{dts|format=dmy|2021|09|02}}<ref>{{cite web|url=https://lists.strace.io/pipermail/strace-devel/2021-September/010674.html|title=strace 5.14 released|author=Dmitry V. Levin|date=2021-09-02}}</ref>
 | Added support for the new <code>memfd_secret</code> and <code>quotactl_fd</code> syscalls decoding
 |-
 | 5.13 || {{dts|format=dmy|2021|07|18}}<ref>{{cite web|url=https://lists.strace.io/pipermail/strace-devel/2021-July/010613.html|title=strace 5.13 released|author=Dmitry V. Levin|date=2021-07-18}}</ref>
 | Implemented System Call Vectored ABI support on the IBM POWER architecture
 |-
 | 5.12 || {{dts|format=dmy|2021|04|26}}<ref>{{cite web|url=https://lists.strace.io/pipermail/strace-devel/2021-April/010516.html|title=strace 5.12 released|author=Dmitry V. Levin|date=2021-04-26}}</ref>
 | Added support for the new <code>mount_setattr</code> syscall decoding
 |-
 | 5.11 || {{dts|format=dmy|2021|02|17}}<ref>{{cite web|url=https://lists.strace.io/pipermail/strace-devel/2021-February/010405.html|title=strace 5.11 released|author=Dmitry V. Levin|date=2021-02-17}}</ref>
 | Added option for injecting data on syscall entry/exit (<code>poke_enter=</code> and <code>poke_exit=</code> parameters of the <code>--inject</code> option); added support for the new <code>epoll_pwait2</code> syscall decoding; imlemented decoding of <code>FS_IOC_FS[GS]ETXATTR</code>, <code>FS_IOC{,32}_[GS]ETFLAGS</code>, <code>GPIO_*</code>, <code>SIOCADDMULTI</code>, <code>SIOCDELMULTI</code>, <code>SIOCGIFENCAP</code>, <code>SIOCOUTQNSD</code>, <code>SIOCSIFENCAP</code>, <code>SIOCSIFHWBROADCAST</code>, <code>UBI_IOCRPEB</code>, <code>UBI_IOCSPEB</code>, <code>V4L2_BUF_TYPE_META_CAPTURE</code>, <code>V4L2_BUF_TYPE_META_OUTPUT</code>, and <code>VIDIOC_QUERY_EXT_CTRL</code> ioctl commands
 |-
 | 5.10 || {{dts|format=dmy|2020|12|14}}<ref>{{cite web|url=https://lists.strace.io/pipermail/strace-devel/2020-December/010295.html|title=strace 5.10 released|author=Dmitry V. Levin|date=2020-12-14}}</ref>
 | Stack tracing is supported for non-native personalities when compiled with [[GNU Binutils#elfutils|<code>libdw</code>]];  added support for <code>process_madvise</code> syscall decoding
 |-
 | 5.9 || {{dts|format=dmy|2020|09|24}}<ref>{{cite web|url=https://lists.strace.io/pipermail/strace-devel/2020-September/010250.html|title=strace 5.9 released|author=Dmitry V. Levin|date=2020-09-24}}</ref>
 | Added support for <code>close_range</code> syscall decoding;  added support for [[Trusted execution environment|<code>TEE_*</code>]] ioctl decoding;  implemented decoding of <code>{msg,msq,sem}info</code> and <code>{msg,msq,sem}id_ds</code> structures used in the respective System V IPC syscalls commands
 |-
 | 5.8 || {{dts|format=dmy|2020|08|06}}<ref>{{cite web|url=https://lists.strace.io/pipermail/strace-devel/2020-August/010057.html|title=strace 5.8 released|author=Dmitry V. Levin|date=2020-08-06}}</ref>
 | Changed the list of syscalls covered by the <code>%process</code> group to contain syscalls associated with process lifecycle: <code>kill</code>, <code>tkill</code>, <code>tgkill</code>, <code>pidfd_send_signal</code>, and <code>rt_sigqueueinfo</code> were added, <code>arch_prctl</code> and <code>unshare</code> were removed;  added support for <code>faccessat2</code> syscall decoding;  added support for <code>LOOP_CONFIGURE</code> ioctl decoding
 |-
 | 5.7 || {{dts|format=dmy|2020|06|01}}<ref>{{cite web|url=https://lists.strace.io/pipermail/strace-devel/2020-June/009783.html|title=strace 5.7 released|author=Dmitry V. Levin|date=2020-06-01}}</ref>
 | 
 |-
 | 5.6 || {{dts|format=dmy|2020|04|07}}<ref>{{cite web|url=https://lists.strace.io/pipermail/strace-devel/2020-April/009624.html|title=strace 5.6 released|author=Dmitry V. Levin|date=2020-04-07}}</ref>
 | Added long option aliases along with possibilities for more precise option specifications via <code>-e quiet</code>/<code>--quiet</code>, <code>-e decode-fds</code>/<code>--decode-fds</code>, <code>--absolute-timestamps</code>, <code>--relative-timestamps</code>, and <code>--syscall-times</code> options;  implemented various syscall statistics improvements
 |-
 | 5.5 || {{dts|format=dmy|2020|02|06}}<ref>{{cite web|url=https://lists.strace.io/pipermail/strace-devel/2020-February/009337.html|title=strace 5.5 released|author=Dmitry V. Levin|date=2020-02-06}}</ref>
 | 
 |-
 | 5.4 || {{dts|format=dmy|2019|11|28}}<ref>{{cite web|url=https://lists.strace.io/pipermail/strace-devel/2019-November/009261.html|title=strace 5.4 released|author=Dmitry V. Levin|date=2019-11-28}}</ref>
 |-
 | 5.3 || {{dts|format=dmy|2019|09|25}}<ref>{{cite web|url=https://lists.strace.io/pipermail/strace-devel/2019-September/009155.html|title=strace 5.3 released|author=Dmitry V. Levin|date=2019-09-25}}</ref>
 |-
 | 5.2 || {{dts|format=dmy|2019|07|12}}<ref>{{cite web|url=https://lists.strace.io/pipermail/strace-devel/2019-July/008954.html|title=strace 5.2 released|author=Dmitry V. Levin|date=2019-07-12}}</ref>
 |-
 | 5.1 || {{dts|format=dmy|2019|05|22}}<ref>{{cite web|url=https://lists.strace.io/pipermail/strace-devel/2019-May/008778.html|title=strace 5.1 released|author=Dmitry V. Levin|date=2019-05-22}}</ref>
 |-
 | 5.0 || {{dts|format=dmy|2019|03|19}}<ref>{{cite web|url=https://lists.strace.io/pipermail/strace-devel/2019-March/008672.html|title=strace 5.0 released|author=Dmitry V. Levin|date=2019-03-19}}</ref>
 |-
 | 4.26 || {{dts|format=dmy|2018|12|26}}<ref>{{cite web|url=https://lists.strace.io/pipermail/strace-devel/2018-December/008573.html|title=strace 4.26 released|author=Dmitry V. Levin|date=2018-12-26}}</ref>
 |-
 | 4.25 || {{dts|format=dmy|2018|10|30}}<ref>{{cite web|url=https://lists.strace.io/pipermail/strace-devel/2018-October/008399.html|title=strace 4.25 released|author=Dmitry V. Levin|date=2018-10-30}}</ref>
 |-
 | 4.24 || {{dts|format=dmy|2018|08|14}}<ref>{{cite web|url=https://lists.strace.io/pipermail/strace-devel/2018-August/008347.html|title=strace 4.24 released|author=Dmitry V. Levin|date=2018-08-14}}</ref>
 |-
 | 4.23 || {{dts|format=dmy|2018|06|14}}<ref>{{cite web|url=https://lists.strace.io/pipermail/strace-devel/2018-June/008234.html|title=strace 4.23 released|author=Dmitry V. Levin|date=2018-06-14}}</ref>
 |-
 | 4.22 || {{dts|format=dmy|2018|04|05}}<ref>{{cite web|url=https://lists.strace.io/pipermail/strace-devel/2018-April/008110.html|title=strace 4.22 released|author=Dmitry V. Levin|date=2018-04-05}}</ref>
 |-
 | 4.21 || {{dts|format=dmy|2018|02|13}}<ref>{{cite web|url=https://lists.strace.io/pipermail/strace-devel/2018-February/007895.html|title=strace 4.21 released|author=Dmitry V. Levin|date=2018-02-13}}</ref>
 |-
 | 4.20 || {{dts|format=dmy|2017|11|13}}<ref>{{cite web|url=https://lists.strace.io/pipermail/strace-devel/2017-November/007696.html|title=strace 4.20 released|author=Dmitry V. Levin|date=2017-11-13}}</ref>
 |-
 | 4.19 || {{dts|format=dmy|2017|09|05}}<ref>{{cite web|url=https://lists.strace.io/pipermail/strace-devel/2017-September/007596.html|title=strace 4.19 released|author=Dmitry V. Levin|date=2017-09-05}}</ref>
 |-
 | 4.18 || {{dts|format=dmy|2017|07|05}}<ref>{{cite web|url=https://lists.strace.io/pipermail/strace-devel/2017-July/006897.html|title=strace 4.18 released|author=Dmitry V. Levin|date=2017-07-05}}</ref>
 |-
 | 4.17 || {{dts|format=dmy|2017|05|24}}<ref>{{cite web|url=https://lists.strace.io/pipermail/strace-devel/2017-May/006415.html|title=strace 4.17 released|author=Dmitry V. Levin|date=2017-05-24}}</ref>
 |-
 | 4.16 || {{dts|format=dmy|2017|02|14}}<ref>{{cite web|url=https://lists.strace.io/pipermail/strace-devel/2017-February/005995.html|title=strace 4.16 released|author=Dmitry V. Levin|date=2017-02-14}}</ref>
 |-
 | 4.15 || {{dts|format=dmy|2016|12|14}}<ref>{{cite web|url=https://lists.strace.io/pipermail/strace-devel/2016-December/005841.html|title=strace 4.15 released|author=Dmitry V. Levin|date=2016-12-14}}</ref>
 |-
 | 4.14 || {{dts|format=dmy|2016|10|04}}<ref>{{cite web|url=https://lists.strace.io/pipermail/strace-devel/2016-October/005679.html|title=strace 4.14 released|author=Dmitry V. Levin|date=2016-10-04}}</ref>
 |-
 | 4.13 || {{dts|format=dmy|2016|07|26}}<ref>{{cite web|url=https://lists.strace.io/pipermail/strace-devel/2016-July/005406.html|title=strace 4.13 released|author=Dmitry V. Levin|date=2016-07-26}}</ref>
 |-
 | 4.12 || {{dts|format=dmy|2016|05|31}}<ref>{{cite web|url=https://lists.strace.io/pipermail/strace-devel/2016-May/005205.html|title=strace 4.12 released|author=Dmitry V. Levin|date=2016-05-31}}</ref>
 |-
 | 4.11 || {{dts|format=dmy|2015|12|21}}<ref>{{cite web|url=https://lists.strace.io/pipermail/strace-devel/2015-December/004428.html|title=strace 4.11 released|author=Dmitry V. Levin|date=2015-12-21}}</ref>
 |-
 | 4.10 || {{dts|format=dmy|2015|03|06}}<ref>{{cite web|url=https://lists.strace.io/pipermail/strace-devel/2015-March/003953.html|title=strace 4.10 released|author=Dmitry V. Levin|date=2015-03-06}}</ref>
 |-
 | 4.9 || {{dts|format=dmy|2014|08|15}}<ref>{{cite web|url=https://lists.strace.io/pipermail/strace-devel/2014-August/003500.html|title=strace 4.9 released|author=Dmitry V. Levin|date=2014-08-15}}</ref>
 |-
 | 4.8 || {{dts|format=dmy|2013|06|03}}<ref>{{cite web|url=https://lists.strace.io/pipermail/strace-devel/2013-June/002656.html|title=strace 4.8 released|author=Dmitry V. Levin|date=2013-06-03}}</ref>
 |-
 | 4.7 || {{dts|format=dmy|2012|05|02}}<ref>{{cite web|url=https://lists.strace.io/pipermail/strace-devel/2012-May/002292.html|title=strace 4.7 released|author=Dmitry V. Levin|date=2012-05-02}}</ref> 
 | All non-Linux code had been removed
 |-
 | 4.6 || {{dts|format=dmy|2011|03|15}}<ref>{{cite web|url=https://lists.strace.io/pipermail/strace-devel/2011-March/001803.html|title=strace 4.6 released|author=Dmitry V. Levin|date=2011-03-15}}</ref>
 |-
 | 4.5.20 || {{dts|format=dmy|2010|04|13}}
 | Added support for new <code>inotify_init1</code>, <code>perf_event_open</code>, <code>preadv</code>, <code>pwritev</code>, <code>recvmmsg</code>, <code>rt_tgsigqueueinfo</code> syscalls on Linux; <code>-C</code> option added, that combines regular and summary output;  added Tile architecture support on Linux
 |-
 | 4.5.19 || {{dts|format=dmy|2009|10|21}}
 | Maintainership passed to Dmitry Levin;  strace now terminates with the same exit code/signal as the traced program (if it was started by strace);  added support for new <code>accept4</code>, <code>dup3</code>, <code>epoll_create1</code>, <code>eventfd2</code>, <code>inotify_init1</code>, <code>pipe2</code>, <code>signalfd4</code> syscalls on Linux;  added Blackfin, AVR32, and CRIS architedcture support on Linux
 |-
 | 4.5.18 || {{dts|format=dmy|2008|08|28}}
 | Added support for <code>subpage_prot</code> POWER-specific syscall on Linux
 |-
 | 4.5.17 || {{dts|format=dmy|2008|07|21}}
 | <code>-F</code> flag is deprecated, as <code>-f</code> traces <code>vfork</code> on Linux since long time
 |-
 | 4.5.16 || {{dts|format=dmy|2007|08|03}}
 | 
 |-
 | 4.5.15 || {{dts|format=dmy|2007|01|16}}
 | Added support for new <code>*at</code>, <code>inotify*</code>, <code>pselect6</code>, <code>ppoll</code> and <code>unshare</code> syscalls on Linux
 |-
 | 4.5.14 || {{dts|format=dmy|2007|01|16}}
 | System call number can be supplied in <code>-e</code> specification
 |-
 | 4.5.13 || {{dts|format=dmy|2005|08|03}}
 | Add <code>desc</code> syscall group support to <code>-e trace=</code>
 |-
 | 4.5.12 || {{dts|format=dmy|2005|06|08}}
 |
 |-
 | 4.5.11 || {{dts|format=dmy|2005|03|22}}
 |
 |-
 | 4.5.10 || {{dts|format=dmy|2005|03|13}}
 |
 |-
 | 4.5.9  || {{dts|format=dmy|2004|02|04}}
 |
 |-
 | 4.5.8  || {{dts|format=dmy|2004|10|19}}
 | Decode <code>mbind</code>, <code>[sg]et_mempolicy</code>, <code>waitid</code>, <code>fadvise64{,_64}</code>, and <code>epoll_*</code> syscalls, <code>RTC_*</code> ioctls on Linux
 |-
 | 4.5.7  || {{dts|format=dmy|2004|08|31}}
 | 
 |-
 | 4.5.6  || {{dts|format=dmy|2004|07|12}}
 | Added support for 64-bit SPARC architecture on Linux.
 |-
 | 4.5.5  || {{dts|format=dmy|2004|06|27}}
 | 
 |-
 | 4.5.4  || {{dts|format=dmy|2004|06|03}}
 | <code>-p</code> attaches to all NPTL threads on Linux only when <code>-f</code> is supplied
 |-
 | 4.5.3  || {{dts|format=dmy|2004|04|16}}
 | Added support for <code>mq_*</code> syscalls on Linux;  <code>-p</code> now attaches to all NPTL threads on Linux
 |-
 | 4.5.2  || {{dts|format=dmy|2004|03|01}}
 | 
 |-
 | 4.5.1  || {{dts|format=dmy|2003|11|13}}
 | 
 |-
 | 4.5    || {{dts|format=dmy|2003|09|24}}
 | Maintainership passed to Roland McGrath;  added x86-64 support on Linux with support of tracing of compat processes;  added support for SH and SH64 architectures on Linux;  <code>-E</code> option added
 |-
 | 4.4    || {{dts|format=dmy|2001|08|19}}
 | 
 |-
 | 4.3.1  || {{dts|format=dmy|2001|04|07}}
 | 
 |-
 | 4.3    || {{dts|format=dmy|2001|04|01}}
 | Added support for HP PA/RISC and IA-64 architectures on Linux;  added support for 32-bit UID/GID syscalls on Linux;  added support for FreeBSD on x86
 |-
 | 4.2    || {{dts|format=dmy|2000|01|21}}
 | Added support for IBM Z architecture on Linux
 |-
 | 4.1    || {{dts|format=dmy|1999|11|26}}
 | Added support for MIPS architecture on Linux;  <code>strace-graph</code> script added
 |-
 | 4.0.1  || {{dts|format=dmy|1999|07|25}}
 | 
 |-
 | 4.0    || {{dts|format=dmy|1999|07|09}}
 | Fixed 64-bit <code>struct stat</code> decoding on Linux;  Irix 64 updates;  Solaris updates
 |-
 | 3.99.1 || {{dts|format=dmy|1999|06|09}}
 | 
 |-
 | 3.99   || {{dts|format=dmy|1999|04|27}}
 | New maintainer, Wichert Akkerman; added support for IBM POWER, SPARC, and ARM architectures on Linux;  added support for many syscalls on Linux
 |-
 | 3.1    || {{dts|format=dmy|1996|06|01}}
 | Added support for the Irix OS, m68k and DEC Alpha architectures on Linux; added support for <code>-o!</code> option syntax; added support for syscall classes (<code>file</code>, <code>process</code>);  added support for IPC syscalls on Sun OS
 |-
 | 3.0    || {{dts|format=dmy|1994|07|09}}<ref>{{cite web|url=https://groups.google.com/forum/#!topic/comp.sources.misc/ScA8PaNwsBU|title=v43i075: strace - system call tracer for sunos, linux, svr4, solaris2, Part01/10|author=Rick Sladkey|date=1994-07-09}}</ref>
 | Initial cross-platform version by Richard Sladkey. Includes support for <code>-x</code>, <code>-q</code>, <code>-e</code> (<code>trace</code>, <code>abbrev</code>, <code>verbose</code>, <code>raw</code>, <code>signal</code>, <code>read</code>, and <code>write</code> qualifiers), <code>-c</code>, <code>-i</code> options
 |}

== Usage and features ==
The most common use is to start a program using strace, which prints a list of system calls made by the program. This is useful if the program continually crashes, or does not behave as expected; for example using strace may reveal that the program is attempting to access a file which does not exist or cannot be read.

An alternative application is to use the {{code|-p}} flag to attach to a running process. This is useful if a process has stopped responding, and might reveal, for example, that the process is blocking whilst attempting to make a network connection.

Among other features, strace allows the following:
* Specifying a filter of syscall names that should be traced (via the <code>-e trace=</code> option): by name, like {{Mono|clone,fork,vfork}}; using one of the predefined groups, like {{Mono|%ipc}} or {{Mono|%file}}; or (since strace 4.17) using regular expression syntax, like <code>-e trace=/clock_.*</code>.
* Specifying a list of paths to be traced (<code>-P /etc/ld.so.cache</code>, for example).
* Specifying a list of file descriptors whose I/O should be dumped (<code>-e read=</code> and <code>-e write=</code> options).
* Counting syscall execution time and count (<code>-T</code>, <code>-c</code>, <code>-C</code>, and <code>-w</code> options;  <code>-U</code> option enables printing of additional information, like minimum and maximum syscall execution time).
* Printing relative or absolute time stamps (<code>-t</code> and <code>-r</code> options).
* Tampering with the syscalls being executed (<code>-e inject=''syscall specification'':''tampering specification''</code> option): modifying return (<code>:retval=</code>;  since strace 4.16) and error code (<code>:error=</code>;  since strace 4.15) of the specified syscalls, inject signals (<code>:signal=</code>;  since strace 4.16), delays (<code>:delay_enter=</code> and <code>:delay_exit=</code>;  since strace 4.22), and modify data pointed by syscall arguments (<code>:poke_enter=</code> and <code>:poke_exit=</code>;  since strace 5.11) upon their execution.
* Extracting information about file descriptors (including sockets, <code>-y</code> option;  <code>-yy</code> option provides some additional information, like endpoint addresses for sockets, paths and device major/minor numbers for files).
* Printing stack traces, including (since strace 4.21) symbol demangling (<code>-k</code> option).
* Filtering by syscall return status (<code>-e status=</code> option; since strace 5.2<ref group="note">Its shorthand for showing only successful calls, <code>-z</code> option, was originally added in strace 4.5, but was never documented as it did not work properly.</ref>).
* Perform translation of thread, process, process group, and session IDs appearing in the trace into strace's [[Linux namespaces#Process ID (pid)|PID namespace]] (<code>--pidns-translation</code> option;  since strace 5.9).
* Decoding [[SELinux]] context information associated with processes, files, and descriptors (<code>--secontext</code> option;  since strace 5.12).

strace supports decoding of arguments of some classes of [[ioctl]] commands, such as [[btrfs|BTRFS_*]], [[Video4Linux|V4L2_*]], [[Device mapper|DM_*]], [[Linux namespaces|NSFS_*]], [[Memory Technology Device|MEM*]], [[evdev|EVIO*]], [[Kernel-based Virtual Machine|KVM_*]], and several others;  it also supports decoding of various [[netlink]] protocols.

As strace only details system calls, it cannot be used to detect as many problems as a code debugger such as [[GNU Debugger]] (gdb). It is, however, easier to use than a code debugger, and is a very useful tool for system administrators. It is also used by researchers to generate system call traces for later ''system call replay''.<ref name=Horky13>
{{cite web
|last = Horky
|first = Jiri
| year = 2013
| title = The ioapps IO profiler and IO traces replayer
| url = http://code.google.com/p/ioapps/
| accessdate = 2013-09-16}}
</ref><ref name=Waterland07>
{{cite web
|last = Waterland
|first = Amos
|year = 2007
| title = The sreplay system call replayer
| url = http://people.seas.harvard.edu/~apw/sreplay/
| accessdate = 2013-09-16}}
</ref><ref name=Burton98>
{{cite web
|last = Burton
|first = Ariel
|year = 1998
| title = Workload characterization using lightweight system call tracing and reexecution
| url = http://www.doc.ic.ac.uk/~phjk/Publications/WkldChctrsnUsngTracesReex.pdf
| accessdate = 2013-09-16}}
</ref>

== Examples ==
The following is an example of typical output of the <code>strace</code> command:

<syntaxhighlight lang="console">
user@server:~$ strace ls
...
open(".", O_RDONLY|O_NONBLOCK|O_LARGEFILE|O_DIRECTORY|O_CLOEXEC) = 3
fstat64(3, {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
fcntl64(3, F_GETFD)                     = 0x1 (flags FD_CLOEXEC)
getdents64(3, /* 18 entries */, 4096)   = 496
getdents64(3, /* 0 entries */, 4096)    = 0
close(3)                                = 0
fstat64(1, {st_mode=S_IFIFO|0600, st_size=0, ...}) = 0
mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb7f2c000
write(1, "autofs\nbackups\ncache\nflexlm\ngames"..., 86autofsA
</syntaxhighlight>

The above fragment is only a small part of the output of strace when run on the '[[ls]]' command. It shows that the current working directory is opened, inspected and its contents retrieved. The resulting list of file names is written to standard output.

== {{Anchor|XTRACE}}Similar tools ==
Different operating systems feature other similar or related [[Instrumentation (computer programming)|instrumentation]] tools, offering similar or more advanced features; some of the tools (although using the same or a similar name) may use completely different work mechanisms, resulting in different feature sets or results.  Such tools include the following:

* [[Linux]] has [[ltrace]] that can trace library and system calls, ''xtrace'' that can trace [[X Window System]] programs,<ref>{{cite web |url=http://xtrace.alioth.debian.org/ |title=XTrace - trace X protocol connections |website=xtrace.alioth.debian.org |date= |accessdate=2014-08-12 |archive-date=2014-08-05 |archive-url=https://web.archive.org/web/20140805180608/http://xtrace.alioth.debian.org/ |url-status=dead }}</ref> [[SystemTap]], [[perf (Linux)|perf]], and [[trace-cmd]] and [[KernelShark]] that extend [[ftrace]].
* [[AIX]] provides the {{Mono|truss}} command
* [[HP-UX]] offers the {{Mono|[[Tusc (Unix)|Tusc]]}} command
* [[Solaris (operating system)|Solaris]] / [[Illumos]] has truss and [[DTrace]]
* [[UnixWare]] provides the {{Mono|truss}} command
* [[FreeBSD]] provides the {{Mono|truss}} command, [[ktrace]] and [[DTrace]]
* [[NetBSD]] provides [[ktrace]] and DTrace
* [[OpenBSD]] uses [[ktrace]] and kdump
* [[macOS]] provides [[ktrace]] (10.4 and earlier), DTrace (from Solaris) and associated dtruss in 10.5 and later.<ref>{{cite web|url=https://developer.apple.com/library/mac/documentation/Darwin/Reference/ManPages/man1/dtrace.1.html |title=dtrace(1) Mac OS X Manual Page |publisher=Developer.apple.com |date= |accessdate=2014-07-23}}</ref>
* [[Microsoft Windows]] has a similar utility called StraceNT, written by Pankaj Garg,<ref>{{cite web|url=http://intellectualheaven.com/default.asp?BH=StraceNT|title=IntellectualHeaven - Strace For Windows|work=intellectualheaven.com|accessdate=29 January 2015|archive-date=5 March 2016|archive-url=https://web.archive.org/web/20160305001814/http://intellectualheaven.com/default.asp?BH=StraceNT|url-status=dead}}</ref> and a similar [[GUI]]-based utility called [[Process Monitor]], developed by [[Sysinternals]].

==See also==
{{Portal|Free and open-source software|Computer programming}}
* [[gdb]]
* [[List of Unix commands]]
* [[lsof]]

== Notes ==
{{Reflist|group="note"}}

== References ==
{{Reflist|30em}}

==External links==
* [https://strace.io/ strace project page]
* [http://man7.org/linux/man-pages/man1/strace.1.html Manual page]
* [http://www.osreviews.net/reviews/admin/strace OS Reviews article on strace]
* [http://man7.org/conf/ndctechtown2018/system_call_tracing_with_strace-NDC-TechTown-Kerrisk.pdf "System Call Tracing with strace"], a talk with an overview of strace features and usage, given by [[Michael Kerrisk]] at [https://ndctechtown.com/ NDC TechTown] 2018
* [https://static.sched.com/hosted_files/devconfcz2019/a8/devconfcz_2019-slides-modern_strace.pdf "Modern strace"] ([https://gitlab.com/strace/strace-talks/tree/master/2019-devconf.cz-brno-modern_strace source]), a talk with an overview of strace features, given by Dmitry Levin at [[DevConf.cz]] 2019

[[Category:Command-line software]]
[[Category:Debuggers]]
[[Category:Free software programmed in C]]
[[Category:Software using the GNU Lesser General Public License]]
[[Category:Unix programming tools]]