From debbugs-submit-bounces@debbugs.gnu.org Fri Jan 19 13:22:50 2018 Received: (at submit) by debbugs.gnu.org; 19 Jan 2018 18:22:50 +0000 Received: from localhost ([127.0.0.1]:35229 helo=debbugs.gnu.org) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from ) id 1ecbJS-0000SS-1S for submit@debbugs.gnu.org; Fri, 19 Jan 2018 13:22:50 -0500 Received: from eggs.gnu.org ([208.118.235.92]:43433) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from ) id 1ecbGC-0000NG-Ew for submit@debbugs.gnu.org; Fri, 19 Jan 2018 13:19:28 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ecbG5-0006em-QQ for submit@debbugs.gnu.org; Fri, 19 Jan 2018 13:19:23 -0500 X-Spam-Checker-Version: SpamAssassin 3.3.2 (2011-06-06) on eggs.gnu.org X-Spam-Level: X-Spam-Status: No, score=0.8 required=5.0 tests=BAYES_50,FREEMAIL_FROM, WEIRD_QUOTING autolearn=disabled version=3.3.2 Received: from lists.gnu.org ([2001:4830:134:3::11]:47020) by eggs.gnu.org with esmtps (TLS1.0:RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1ecbG5-0006ei-Mh for submit@debbugs.gnu.org; Fri, 19 Jan 2018 13:19:21 -0500 Received: from eggs.gnu.org ([2001:4830:134:3::10]:34391) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ecbG3-0004uB-Lx for bug-coreutils@gnu.org; Fri, 19 Jan 2018 13:19:21 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ecbFz-0006cs-Nm for bug-coreutils@gnu.org; Fri, 19 Jan 2018 13:19:19 -0500 Received: from mout.web.de ([212.227.15.3]:53337) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_128_CBC_SHA1:16) (Exim 4.71) (envelope-from ) id 1ecbFz-0006cN-D4 for bug-coreutils@gnu.org; Fri, 19 Jan 2018 13:19:15 -0500 Received: from [5.147.253.138] ([5.147.253.138]) by 3c-app-webde-bs06.server.lan (via HTTP); Fri, 19 Jan 2018 19:19:13 +0100 MIME-Version: 1.0 Message-ID: From: devzero@web.de To: bug-coreutils@gnu.org Subject: shred bug - 1st byte written is wrong sometimes Content-Type: text/plain; charset=UTF-8 Date: Fri, 19 Jan 2018 19:19:13 +0100 Importance: normal Sensitivity: Normal Content-Transfer-Encoding: quoted-printable X-Priority: 3 X-Provags-ID: V03:K1:3bylBoaz0wFng5QeTly7BIidWWMoLRAxx2vjI5zeL+D NU6ywL4vtqMobHFmDMfVPv7UTYnUiZnCTSWHDksSWIc5mJDVsm ePB2dUCKuajcbEijLPs8V0oncyzVSOBbFFkHthrhBlDM7dbgKJ 50ku4JPgsQxm/b80AWwimCEQVE101LXGxgO0RFJjsehBAhKMMI W4aiT2V8Fvt+4cuJkayoJ7ZAYmbkiMXAw00Bhn6EhWXTtNLYtR LzsJ1NRfreOrxNOdWddhTSy0+z1V1TTQ6C0hL1hRJ8JpnGn/uP JMDuts= X-UI-Out-Filterresults: notjunk:1;V01:K0:7+YJ6i4eNRI=:VJFlZLYpSrAm9R1vss+BTI EcuiuUCpoQpNzmPxfFlfB9mNvjz5/oS3XBGt8rZrrePE1cU1sCTmDStA0VYFyfFJLPgrDMrik TnRuI0XrWiLxHTF00KhnFMutlMzW9lxBVFG3a2DYN/ZT5RPKWXKcS0LzlG2L2f41i5wA6k3ln oN/XrpV0Z2Ayg2rGuThOjsNA4eQCYqghuGTYiaOKsM7iWfEopaYXdyIY0Z/vCFsTjktPHmco1 Qkh3bUMLc3bcK7iKEK07c85RW9UwrOE3CptvaIS5Zvtn6UZIjLtkDGbCKEnp5IolETUBI2PQm 7FIXU+HzljHKtN4wrlFIUaLw0ldPeU4JC0SkUeHzsdSXd+OcCX0kuQs0PccgQ0iJC41MMmVH3 6YT/FqsCqDYteRTdvVnwVMIK9uQVFgJs3CPw7cl8cXedM730wsuPf0wKzGJk9rg5I+CTpFo73 d+f4s/2BgcxQWnVqjmVNfod2q5184tDUKVOqnUsh2g0S+wOLS/8u X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.6.x X-Received-From: 2001:4830:134:3::11 X-Spam-Score: -4.1 (----) X-Debbugs-Envelope-To: submit X-Mailman-Approved-At: Fri, 19 Jan 2018 13:22:48 -0500 X-BeenThere: debbugs-submit@debbugs.gnu.org X-Mailman-Version: 2.1.18 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: debbugs-submit-bounces@debbugs.gnu.org Sender: "Debbugs-submit" X-Spam-Score: -4.1 (----) Hi, i`m testing wear-levelling of an SLC USB Stick (cheap one i want to use them for long-term data-logging) and found shred to be a useful and fast utility to repeatedly overwrite a file's region (the=20 datalogger i'm building will use rrdtool) As i already did some other testing before, shred made me believe my usb stick would already be "worn out", because i was seeing 1st=20 byte flip occasionally when taking a look into the written data with=20 xxd=2E I investigated and as you can see below, when repeatedly writing to=20 the same file with shred, we can see with strace that shred is doing=20 wrong=2E Looks like a bug to me=2E I tested this on recent CentOS7 (shred 8=2E22) and older Ubuntu based system with shred 8=2E25=2E I also compiled coreutils 8=2E29 and tested with the recent shred release - they all show this behaviour=2E regards Roland shred -n 10000000 -s 100 file & # cat file |xxd 0000000: 7fff ffff ffff ffff ffff ffff ffff ffff =2E=2E=2E=2E=2E=2E=2E=2E= =2E=2E=2E=2E=2E=2E=2E=2E <- (!) 0000010: ffff ffff ffff ffff ffff ffff ffff ffff =2E=2E=2E=2E=2E=2E=2E=2E= =2E=2E=2E=2E=2E=2E=2E=2E 0000020: ffff ffff ffff ffff ffff ffff ffff ffff =2E=2E=2E=2E=2E=2E=2E=2E= =2E=2E=2E=2E=2E=2E=2E=2E 0000030: ffff ffff ffff ffff ffff ffff ffff ffff =2E=2E=2E=2E=2E=2E=2E=2E= =2E=2E=2E=2E=2E=2E=2E=2E 0000040: ffff ffff ffff ffff ffff ffff ffff ffff =2E=2E=2E=2E=2E=2E=2E=2E= =2E=2E=2E=2E=2E=2E=2E=2E 0000050: ffff ffff ffff ffff ffff ffff ffff ffff =2E=2E=2E=2E=2E=2E=2E=2E= =2E=2E=2E=2E=2E=2E=2E=2E 0000060: ffff ffff =2E=2E=2E=2E # cat file |xxd 0000000: 2492 4924 9249 2492 4924 9249 2492 4924 $=2EI$=2EI$=2EI$=2EI$=2EI= $ 0000010: 9249 2492 4924 9249 2492 4924 9249 2492 =2EI$=2EI$=2EI$=2EI$=2EI$= =2E 0000020: 4924 9249 2492 4924 9249 2492 4924 9249 I$=2EI$=2EI$=2EI$=2EI$=2E= I 0000030: 2492 4924 9249 2492 4924 9249 2492 4924 $=2EI$=2EI$=2EI$=2EI$=2EI= $ 0000040: 9249 2492 4924 9249 2492 4924 9249 2492 =2EI$=2EI$=2EI$=2EI$=2EI$= =2E 0000050: 4924 9249 2492 4924 9249 2492 4924 9249 I$=2EI$=2EI$=2EI$=2EI$=2E= I 0000060: 2492 4924 $=2EI$ # cat file |xxd 0000000: aaaa aaaa aaaa aaaa aaaa aaaa aaaa aaaa =2E=2E=2E=2E=2E=2E=2E=2E= =2E=2E=2E=2E=2E=2E=2E=2E 0000010: aaaa aaaa aaaa aaaa aaaa aaaa aaaa aaaa =2E=2E=2E=2E=2E=2E=2E=2E= =2E=2E=2E=2E=2E=2E=2E=2E 0000020: aaaa aaaa aaaa aaaa aaaa aaaa aaaa aaaa =2E=2E=2E=2E=2E=2E=2E=2E= =2E=2E=2E=2E=2E=2E=2E=2E 0000030: aaaa aaaa aaaa aaaa aaaa aaaa aaaa aaaa =2E=2E=2E=2E=2E=2E=2E=2E= =2E=2E=2E=2E=2E=2E=2E=2E 0000040: aaaa aaaa aaaa aaaa aaaa aaaa aaaa aaaa =2E=2E=2E=2E=2E=2E=2E=2E= =2E=2E=2E=2E=2E=2E=2E=2E 0000050: aaaa aaaa aaaa aaaa aaaa aaaa aaaa aaaa =2E=2E=2E=2E=2E=2E=2E=2E= =2E=2E=2E=2E=2E=2E=2E=2E 0000060: aaaa aaaa =2E=2E=2E=2E # cat file |xxd 0000000: b6db 6db6 db6d b6db 6db6 db6d b6db 6db6 =2E=2Em=2E=2Em=2E=2Em=2E= =2Em=2E=2Em=2E 0000010: db6d b6db 6db6 db6d b6db 6db6 db6d b6db =2Em=2E=2Em=2E=2Em=2E=2Em= =2E=2Em=2E=2E 0000020: 6db6 db6d b6db 6db6 db6d b6db 6db6 db6d m=2E=2Em=2E=2Em=2E=2Em=2E= =2Em=2E=2Em 0000030: b6db 6db6 db6d b6db 6db6 db6d b6db 6db6 =2E=2Em=2E=2Em=2E=2Em=2E= =2Em=2E=2Em=2E 0000040: db6d b6db 6db6 db6d b6db 6db6 db6d b6db =2Em=2E=2Em=2E=2Em=2E=2Em= =2E=2Em=2E=2E 0000050: 6db6 db6d b6db 6db6 db6d b6db 6db6 db6d m=2E=2Em=2E=2Em=2E=2Em=2E= =2Em=2E=2Em 0000060: b6db 6db6 =2E=2Em=2E # cat file |xxd 0000000: 6eee eeee eeee eeee eeee eeee eeee eeee n=2E=2E=2E=2E=2E=2E=2E=2E= =2E=2E=2E=2E=2E=2E=2E <- (!) 0000010: eeee eeee eeee eeee eeee eeee eeee eeee =2E=2E=2E=2E=2E=2E=2E=2E= =2E=2E=2E=2E=2E=2E=2E=2E 0000020: eeee eeee eeee eeee eeee eeee eeee eeee =2E=2E=2E=2E=2E=2E=2E=2E= =2E=2E=2E=2E=2E=2E=2E=2E 0000030: eeee eeee eeee eeee eeee eeee eeee eeee =2E=2E=2E=2E=2E=2E=2E=2E= =2E=2E=2E=2E=2E=2E=2E=2E 0000040: eeee eeee eeee eeee eeee eeee eeee eeee =2E=2E=2E=2E=2E=2E=2E=2E= =2E=2E=2E=2E=2E=2E=2E=2E 0000050: eeee eeee eeee eeee eeee eeee eeee eeee =2E=2E=2E=2E=2E=2E=2E=2E= =2E=2E=2E=2E=2E=2E=2E=2E 0000060: eeee eeee =2E=2E=2E=2E # cat file |xxd 0000000: a222 2222 2222 2222 2222 2222 2222 2222 =2E""""""""""""""" <- (!) 0000010: 2222 2222 2222 2222 2222 2222 2222 2222 """""""""""""""" 0000020: 2222 2222 2222 2222 2222 2222 2222 2222 """""""""""""""" 0000030: 2222 2222 2222 2222 2222 2222 2222 2222 """""""""""""""" 0000040: 2222 2222 2222 2222 2222 2222 2222 2222 """""""""""""""" 0000050: 2222 2222 2222 2222 2222 2222 2222 2222 """""""""""""""" 0000060: 2222 2222 # dd if=3D/dev/urandom of=3D/tmp/file bs=3D1k count=3D1 ; strace -f -xx -e= write=3Dall shred -n 10000000 -s 100 /tmp/file 2>&1 |grep -A1 "write(3" |h= ead -n 50 1+0 Datens=C3=A4tze ein 1+0 Datens=C3=A4tze aus 1024 Bytes (1,0 kB) kopiert, 0,000307051 s, 3,3 MB/s write(3, "\x39\x75\x95\xd8\xfa\x3b\xf4\xdf\x11\x09\x66\xae\x2a\x14\x4f\x24= \x74\xa9\x96\x69\x3e\xe7\xb6\x75\x22\x39\x76\xee\xa6\xf8\x22\xb7"=2E=2E=2E,= 100) =3D -1 EINVAL (Invalid argument) fcntl(3, F_GETFL) =3D 0xc001 (flags O_WRONLY|O_DIRECT|O_LARGEFILE) -- write(3, "\x39\x75\x95\xd8\xfa\x3b\xf4\xdf\x11\x09\x66\xae\x2a\x14\x4f\x24= \x74\xa9\x96\x69\x3e\xe7\xb6\x75\x22\x39\x76\xee\xa6\xf8\x22\xb7"=2E=2E=2E,= 100) =3D 100 | 00000 39 75 95 d8 fa 3b f4 df 11 09 66 ae 2a 14 4f 24 9u=2E=2E=2E;=2E=2E= =2E=2Ef=2E*=2EO$ | -- write(3, "\x55\x55\x55\x55\x55\x55\x55\x55\x55\x55\x55\x55\x55\x55\x55\x55= \x55\x55\x55\x55\x55\x55\x55\x55\x55\x55\x55\x55\x55\x55\x55\x55"=2E=2E=2E,= 100) =3D 100 | 00000 55 55 55 55 55 55 55 55 55 55 55 55 55 55 55 55 UUUUUUUUUUUUUUUU | -- write(3, "\xcc\xcc\xcc\xcc\xcc\xcc\xcc\xcc\xcc\xcc\xcc\xcc\xcc\xcc\xcc\xcc= \xcc\xcc\xcc\xcc\xcc\xcc\xcc\xcc\xcc\xcc\xcc\xcc\xcc\xcc\xcc\xcc"=2E=2E=2E,= 100) =3D 100 | 00000 cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc =2E=2E=2E=2E=2E=2E= =2E=2E=2E=2E=2E=2E=2E=2E=2E=2E | -- write(3, "\xaa\xaa\xaa\xaa\xaa\xaa\xaa\xaa\xaa\xaa\xaa\xaa\xaa\xaa\xaa\xaa= \xaa\xaa\xaa\xaa\xaa\xaa\xaa\xaa\xaa\xaa\xaa\xaa\xaa\xaa\xaa\xaa"=2E=2E=2E,= 100) =3D 100 | 00000 aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa =2E=2E=2E=2E=2E=2E= =2E=2E=2E=2E=2E=2E=2E=2E=2E=2E | -- write(3, "\x91\x11\x11\x11\x11\x11\x11\x11\x11\x11\x11\x11\x11\x11\x11\x11= \x11\x11\x11\x11\x11\x11\x11\x11\x11\x11\x11\x11\x11\x11\x11\x11"=2E=2E=2E,= 100) =3D 100 <-(!) | 00000 91 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11 =2E=2E=2E=2E=2E=2E= =2E=2E=2E=2E=2E=2E=2E=2E=2E=2E | <-(!) -- write(3, "\x80\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00= \x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00"=2E=2E=2E,= 100) =3D 100 | 00000 80 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 =2E=2E=2E=2E=2E=2E= =2E=2E=2E=2E=2E=2E=2E=2E=2E=2E | -- write(3, "\xa2\x22\x22\x22\x22\x22\x22\x22\x22\x22\x22\x22\x22\x22\x22\x22= \x22\x22\x22\x22\x22\x22\x22\x22\x22\x22\x22\x22\x22\x22\x22\x22"=2E=2E=2E,= 100) =3D 100 <-(!) | 00000 a2 22 22 22 22 22 22 22 22 22 22 22 22 22 22 22 =2E"""""""""""""""= | <-(!) -- write(3, "\x92\x49\x24\x92\x49\x24\x92\x49\x24\x92\x49\x24\x92\x49\x24\x92= \x49\x24\x92\x49\x24\x92\x49\x24\x92\x49\x24\x92\x49\x24\x92\x49"=2E=2E=2E,= 100) =3D 100 | 00000 92 49 24 92 49 24 92 49 24 92 49 24 92 49 24 92 =2EI$=2EI$=2EI$=2E= I$=2EI$=2E | -- write(3, "\xbb\xbb\xbb\xbb\xbb\xbb\xbb\xbb\xbb\xbb\xbb\xbb\xbb\xbb\xbb\xbb= \xbb\xbb\xbb\xbb\xbb\xbb\xbb\xbb\xbb\xbb\xbb\xbb\xbb\xbb\xbb\xbb"=2E=2E=2E,= 100) =3D 100 | 00000 bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb =2E=2E=2E=2E=2E=2E= =2E=2E=2E=2E=2E=2E=2E=2E=2E=2E | -- write(3, "\x11\x11\x11\x11\x11\x11\x11\x11\x11\x11\x11\x11\x11\x11\x11\x11= \x11\x11\x11\x11\x11\x11\x11\x11\x11\x11\x11\x11\x11\x11\x11\x11"=2E=2E=2E,= 100) =3D 100 | 00000 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11 =2E=2E=2E=2E=2E=2E= =2E=2E=2E=2E=2E=2E=2E=2E=2E=2E | -- write(3, "\x87\xc8\x72\xf5\xeb\x3f\x8b\x9c\xa5\xbd\xf1\xc5\xdd\x74\x10\x19= \x6a\xc1\xa5\x5c\xcc\x1f\x99\xba\xe7\x92\x55\x92\x55\xfb\x94\x95"=2E=2E=2E,= 100) =3D 100 | 00000 87 c8 72 f5 eb 3f 8b 9c a5 bd f1 c5 dd 74 10 19 =2E=2Er=2E=2E?=2E= =2E=2E=2E=2E=2E=2Et=2E=2E | -- write(3, "\x92\x49\x24\x92\x49\x24\x92\x49\x24\x92\x49\x24\x92\x49\x24\x92= \x49\x24\x92\x49\x24\x92\x49\x24\x92\x49\x24\x92\x49\x24\x92\x49"=2E=2E=2E,= 100) =3D 100 | 00000 92 49 24 92 49 24 92 49 24 92 49 24 92 49 24 92 =2EI$=2EI$=2EI$=2E= I$=2EI$=2E | -- write(3, "\x66\x66\x66\x66\x66\x66\x66\x66\x66\x66\x66\x66\x66\x66\x66\x66= \x66\x66\x66\x66\x66\x66\x66\x66\x66\x66\x66\x66\x66\x66\x66\x66"=2E=2E=2E,= 100) =3D 100 | 00000 66 66 66 66 66 66 66 66 66 66 66 66 66 66 66 66 ffffffffffffffff | -- write(3, "\x3b\xbb\xbb\xbb\xbb\xbb\xbb\xbb\xbb\xbb\xbb\xbb\xbb\xbb\xbb\xbb= \xbb\xbb\xbb\xbb\xbb\xbb\xbb\xbb\xbb\xbb\xbb\xbb\xbb\xbb\xbb\xbb"=2E=2E=2E,= 100) =3D 100 <-(!) | 00000 3b bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb ;=2E=2E=2E=2E=2E= =2E=2E=2E=2E=2E=2E=2E=2E=2E=2E | <-(!) -- write(3, "\xb3\x33\x33\x33\x33\x33\x33\x33\x33\x33\x33\x33\x33\x33\x33\x33= \x33\x33\x33\x33\x33\x33\x33\x33\x33\x33\x33\x33\x33\x33\x33\x33"=2E=2E=2E,= 100) =3D 100 <-(!) | 00000 b3 33 33 33 33 33 33 33 33 33 33 33 33 33 33 33 =2E333333333333333= | <-(!) -- write(3, "\xaa\xaa\xaa\xaa\xaa\xaa\xaa\xaa\xaa\xaa\xaa\xaa\xaa\xaa\xaa\xaa= \xaa\xaa\xaa\xaa\xaa\xaa\xaa\xaa\xaa\xaa\xaa\xaa\xaa\xaa\xaa\xaa"=2E=2E=2E,= 100) =3D 100 | 00000 aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa =2E=2E=2E=2E=2E=2E= =2E=2E=2E=2E=2E=2E=2E=2E=2E=2E | From debbugs-submit-bounces@debbugs.gnu.org Fri Jan 19 19:21:20 2018 Received: (at 30174) by debbugs.gnu.org; 20 Jan 2018 00:21:20 +0000 Received: from localhost ([127.0.0.1]:35380 helo=debbugs.gnu.org) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from ) id 1ecguO-0004sS-DG for submit@debbugs.gnu.org; Fri, 19 Jan 2018 19:21:20 -0500 Received: from zimbra.cs.ucla.edu ([131.179.128.68]:55114) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from ) id 1ecguL-0004sF-Nf for 30174@debbugs.gnu.org; Fri, 19 Jan 2018 19:21:18 -0500 Received: from localhost (localhost [127.0.0.1]) by zimbra.cs.ucla.edu (Postfix) with ESMTP id D25C5161624; Fri, 19 Jan 2018 16:21:11 -0800 (PST) Received: from zimbra.cs.ucla.edu ([127.0.0.1]) by localhost (zimbra.cs.ucla.edu [127.0.0.1]) (amavisd-new, port 10032) with ESMTP id jpUA5Qx1bjVO; Fri, 19 Jan 2018 16:21:11 -0800 (PST) Received: from localhost (localhost [127.0.0.1]) by zimbra.cs.ucla.edu (Postfix) with ESMTP id 3396D1616A5; Fri, 19 Jan 2018 16:21:11 -0800 (PST) X-Virus-Scanned: amavisd-new at zimbra.cs.ucla.edu Received: from zimbra.cs.ucla.edu ([127.0.0.1]) by localhost (zimbra.cs.ucla.edu [127.0.0.1]) (amavisd-new, port 10026) with ESMTP id qbMflzDP8R43; Fri, 19 Jan 2018 16:21:11 -0800 (PST) Received: from Penguin.CS.UCLA.EDU (Penguin.CS.UCLA.EDU [131.179.64.200]) by zimbra.cs.ucla.edu (Postfix) with ESMTPSA id 1AAA5161624; Fri, 19 Jan 2018 16:21:11 -0800 (PST) Subject: Re: bug#30174: shred bug - 1st byte written is wrong sometimes To: devzero@web.de, 30174@debbugs.gnu.org References: From: Paul Eggert Organization: UCLA Computer Science Department Message-ID: <6142a10d-984a-73bc-16b3-9de19b03f85a@cs.ucla.edu> Date: Fri, 19 Jan 2018 16:21:10 -0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.5.2 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US X-Spam-Score: -2.3 (--) X-Debbugs-Envelope-To: 30174 X-BeenThere: debbugs-submit@debbugs.gnu.org X-Mailman-Version: 2.1.18 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: debbugs-submit-bounces@debbugs.gnu.org Sender: "Debbugs-submit" X-Spam-Score: -2.3 (--) On 01/19/2018 10:19 AM, devzero@web.de wrote: > shred is doing > wrong. > > Looks like a bug to me. I don't see why it is a bug. It does appear to be intended behavior. Look in the source code, at src/shred.c, and look for "Invert the first bit of every sector." From debbugs-submit-bounces@debbugs.gnu.org Fri Jan 19 22:34:04 2018 Received: (at 30174) by debbugs.gnu.org; 20 Jan 2018 03:34:04 +0000 Received: from localhost ([127.0.0.1]:35449 helo=debbugs.gnu.org) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from ) id 1ecjuu-0000tm-GO for submit@debbugs.gnu.org; Fri, 19 Jan 2018 22:34:04 -0500 Received: from mail.magicbluesmoke.com ([82.195.144.49]:42212) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from ) id 1ecjus-0000tT-Vo; Fri, 19 Jan 2018 22:34:03 -0500 Received: from localhost.localdomain (unknown [76.21.115.186]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.magicbluesmoke.com (Postfix) with ESMTPSA id 2F6B499C7; Sat, 20 Jan 2018 03:34:00 +0000 (GMT) Subject: Re: bug#30174: shred bug - 1st byte written is wrong sometimes To: devzero@web.de, 30174@debbugs.gnu.org References: From: =?UTF-8?Q?P=c3=a1draig_Brady?= Message-ID: Date: Fri, 19 Jan 2018 19:33:59 -0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.8.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit X-Spam-Score: 0.0 (/) X-Debbugs-Envelope-To: 30174 X-BeenThere: debbugs-submit@debbugs.gnu.org X-Mailman-Version: 2.1.18 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: debbugs-submit-bounces@debbugs.gnu.org Sender: "Debbugs-submit" X-Spam-Score: 0.0 (/) tag 30174 notabug close 30174 stop On 19/01/18 10:19, devzero@web.de wrote: > Hi, > > i`m testing wear-levelling of an SLC USB Stick (cheap one i want to > use them for long-term data-logging) and found shred to be a useful > and fast utility to repeatedly overwrite a file's region (the > datalogger i'm building will use rrdtool) > > As i already did some other testing before, shred made me believe > my usb stick would already be "worn out", because i was seeing 1st > byte flip occasionally when taking a look into the written data with > xxd. > > I investigated and as you can see below, when repeatedly writing to > the same file with shred, we can see with strace that shred is doing > wrong. > > Looks like a bug to me. > > I tested this on recent CentOS7 (shred 8.22) and older Ubuntu based > system with shred 8.25. I also compiled coreutils 8.29 and tested > with the recent shred release - they all show this behaviour. > > regards > Roland > > > shred -n 10000000 -s 100 file & > > # cat file |xxd > 0000000: 7fff ffff ffff ffff ffff ffff ffff ffff ................ <- (!) This is intentional. >From the source: /* The following patterns have the first bit per 512 byte block flipped */ 8, 0x1000, 0x1249, 0x1492, 0x16DB, 0x1924, 0x1B6D, 0x1DB6, 0x1FFF, 14, 0x1111, 0x1222, 0x1333, 0x1444, 0x1555, 0x1666, 0x1777, 0x1888, 0x1999, 0x1AAA, 0x1BBB, 0x1CCC, 0x1DDD, 0x1EEE, There was no mention why unfortunately. cheers, Pádraig From unknown Mon Jun 23 06:00:26 2025 Received: (at fakecontrol) by fakecontrolmessage; To: internal_control@debbugs.gnu.org From: Debbugs Internal Request Subject: Internal Control Message-Id: bug archived. Date: Sat, 17 Feb 2018 12:24:05 +0000 User-Agent: Fakemail v42.6.9 # This is a fake control message. # # The action: # bug archived. thanks # This fakemail brought to you by your local debbugs # administrator