printf cannot write more than one line to /proc/pid/uid_map
Configuration Information [Automatically generated, do not change]: Machine: x86_64 OS: linux-gnu Compiler: gcc Compilation CFLAGS: -DPROGRAM='bash' -DCONF_HOSTTYPE='x86_64' -DCONF_OSTYPE='linux-gnu' -DCONF_MACHTYPE='x86_64-pc-linux-gnu' -DCONF_VENDOR='pc' -DLOCALEDIR='/usr/share/locale' -DPACKAGE='bash' -DSHELL -DHAVE_CONFIG_H -I. -I../. -I.././include -I.././lib -D_FORTIFY_SOURCE=2 -g -O2 -fstack-protector --param=ssp-buffer-size=4 -Wformat -Werror=format-security -Wall uname output: Linux crescent 3.14.0-rc7 #1 SMP Mon Mar 17 07:17:51 UTC 2014 x86_64 GNU/Linux Machine Type: x86_64-pc-linux-gnu Bash Version: 4.3 Patch Level: 0 Release Status: release Description: Bash's builtin printf cannot write more than one line to /proc/pid/uid_map because printf writes one line at a time and uid_map can be written only once. Repeat-By: shell 1 $ unshare -U $ echo $$ 31861 shell 2 # printf '0 0 1\n1 1 1' > /proc/31861/uid_map printf: write error: Operation not permitted
Re: printf cannot write more than one line to /proc/pid/uid_map
On Tue, Mar 25, 2014 at 08:24:13PM +0900, Kusanagi Kouichi wrote: > Description: > Bash's builtin printf cannot write more than one line to > /proc/pid/uid_map because printf writes one line at a time > and uid_map can be written only once. Sounds like Bash is using the standard I/O library routines, in line buffering mode (i.e. setvbuf(..., _IOLBF, ...); ). It's not clear to me whether this can be considered a bug, as line-buffered output is common, and situations where it fails are rare. > Repeat-By: > # printf '0 0 1\n1 1 1' > /proc/31861/uid_map > printf: write error: Operation not permitted As a workaround, you might consider something like: printf '0 0 1\n1 1 1' | dd bs=1024 > /proc/31861/uid_map
Re: printf cannot write more than one line to /proc/pid/uid_map
On Tue, Mar 25, 2014 at 08:24:13PM +0900, Kusanagi Kouichi wrote: > Configuration Information [Automatically generated, do not change]: > Machine: x86_64 > OS: linux-gnu > Compiler: gcc > Compilation CFLAGS: -DPROGRAM='bash' -DCONF_HOSTTYPE='x86_64' > -DCONF_OSTYPE='linux-gnu' -DCONF_MACHTYPE='x86_64-pc-linux-gnu' > -DCONF_VENDOR='pc' -DLOCALEDIR='/usr/share/locale' -DPACKAGE='bash' -DSHELL > -DHAVE_CONFIG_H -I. -I../. -I.././include -I.././lib -D_FORTIFY_SOURCE=2 > -g -O2 -fstack-protector --param=ssp-buffer-size=4 -Wformat > -Werror=format-security -Wall > uname output: Linux crescent 3.14.0-rc7 #1 SMP Mon Mar 17 07:17:51 UTC 2014 > x86_64 GNU/Linux > Machine Type: x86_64-pc-linux-gnu > > Bash Version: 4.3 > Patch Level: 0 > Release Status: release > > Description: > Bash's builtin printf cannot write more than one line to > /proc/pid/uid_map because printf writes one line at a time > and uid_map can be written only once. I don't see why this is a bash bug though. printf works as documented. The fact that the way it works is incompatible with this /proc thing is *not* bash's fault. It just means that it's not flexible enough to tell it to write all at once, but that's not a bug. > Repeat-By: > shell 1 > $ unshare -U > $ echo $$ > 31861 > > shell 2 > # printf '0 0 1\n1 1 1' > /proc/31861/uid_map > printf: write error: Operation not permitted > -- Eduardo Alan Bustamante López
Re: printf cannot write more than one line to /proc/pid/uid_map
On 2014-03-25 08:58:08 -0500, Dennis Williamson wrote: > On Mar 25, 2014 8:40 AM, "Kusanagi Kouichi" wrote: > > > > Configuration Information [Automatically generated, do not change]: > > Machine: x86_64 > > OS: linux-gnu > > Compiler: gcc > > Compilation CFLAGS: -DPROGRAM='bash' -DCONF_HOSTTYPE='x86_64' > -DCONF_OSTYPE='linux-gnu' -DCONF_MACHTYPE='x86_64-pc-linux-gnu' > -DCONF_VENDOR='pc' -DLOCALEDIR='/usr/share/locale' -DPACKAGE='bash' -DSHELL > -DHAVE_CONFIG_H -I. -I../. -I.././include -I.././lib > -D_FORTIFY_SOURCE=2 -g -O2 -fstack-protector --param=ssp-buffer-size=4 > -Wformat -Werror=format-security -Wall > > uname output: Linux crescent 3.14.0-rc7 #1 SMP Mon Mar 17 07:17:51 UTC > 2014 x86_64 GNU/Linux > > Machine Type: x86_64-pc-linux-gnu > > > > Bash Version: 4.3 > > Patch Level: 0 > > Release Status: release > > > > Description: > > Bash's builtin printf cannot write more than one line to > > /proc/pid/uid_map because printf writes one line at a time > > and uid_map can be written only once. > > > > Repeat-By: > > shell 1 > > $ unshare -U > > $ echo $$ > > 31861 > > > > shell 2 > > # printf '0 0 1\n1 1 1' > /proc/31861/uid_map > > printf: write error: Operation not permitted > > > > What happens if you use /usr/bin/printf instead of the Bash builtin? /usr/bin/printf and dash's printf work as expected.
Re: printf cannot write more than one line to /proc/pid/uid_map
Greg Wooledge writes: > Sounds like Bash is using the standard I/O library routines, in line > buffering mode (i.e. setvbuf(..., _IOLBF, ...); ). See sh_setlinebuf in shell_initialize. Andreas. -- Andreas Schwab, SUSE Labs, sch...@suse.de GPG Key fingerprint = 0196 BAD8 1CE9 1970 F4BE 1748 E4D4 88E3 0EEA B9D7 "And now for something completely different."
Re: printf cannot write more than one line to /proc/pid/uid_map
On 03/25/2014 01:57 PM, Greg Wooledge wrote: > On Tue, Mar 25, 2014 at 08:24:13PM +0900, Kusanagi Kouichi wrote: >> Description: >> Bash's builtin printf cannot write more than one line to >> /proc/pid/uid_map because printf writes one line at a time >> and uid_map can be written only once. > > Sounds like Bash is using the standard I/O library routines, in line > buffering mode (i.e. setvbuf(..., _IOLBF, ...); ). It's not clear > to me whether this can be considered a bug, as line-buffered output > is common, and situations where it fails are rare. > >> Repeat-By: >> # printf '0 0 1\n1 1 1' > /proc/31861/uid_map >> printf: write error: Operation not permitted > > As a workaround, you might consider something like: > > printf '0 0 1\n1 1 1' | dd bs=1024 > /proc/31861/uid_map Note dd will immediately write any short reads in that case too. Though not a specific issue here (since the printf will issue a single write()), to generall get dd to coalesce reads you needs to specify obs separately like: printf '0 0 1\n1 1 1' | dd obs=1024 > /proc/31861/uid_map BTW it's a bit surprising that bash doesn't use standard "default buffering modes" mentioned here: http://www.pixelbeat.org/programming/stdio_buffering/ If you want to use the external printf to achieve more standard buffering modes, you can use `env` like: env printf '%s' '0 0 1\n1 1 1' > /proc/31861/uid_map thanks, Pádraig.
Re: Special built-ins not persisting assignments
On Tue 25 Mar 2014 00:39:18 Pollock, Wayne wrote:
> $ echo $BASH_VERSION
> 4.2.45(1)-release
>
> $ unset foo
>
> $ foo=bar :
>
> $ echo $foo
>
>
> $
>
> ===
>
> According to POSIX/SUS issue 7, assignments for special builtins
> should persist. So the output should be ``bar''.
>
> Is there a setting I should turn off (or need to enable), to
> make this work correctly?
>
> I was able to confirm this bug for version 4.2.37(1)-release as
> well. (zsh 4.3.17 (i386-redhat-linux-gnu) has the same bug.)
as noted, this is a feature of bash :)
POSIX also imposes annoying behavior that bash fixes:
unset foo
f() { :; }
foo=bar f
echo $foo
POSIX will show bar (ugh) while bash will not (yeah!)
-mike
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Re: printf cannot write more than one line to /proc/pid/uid_map
Pádraig Brady writes: > If you want to use the external printf to achieve more > standard buffering modes, you can use `env` like: > > env printf '%s' '0 0 1\n1 1 1' > /proc/31861/uid_map While this will probably work, the more typical way to do this is with command(1P). pgpOycint6nTB.pgp Description: PGP signature
Re: printf cannot write more than one line to /proc/pid/uid_map
-BEGIN PGP SIGNED MESSAGE- Hash: SHA1 On 3/25/14 4:11 PM, Chris Down wrote: > Pádraig Brady writes: >> If you want to use the external printf to achieve more >> standard buffering modes, you can use `env` like: >> >> env printf '%s' '0 0 1\n1 1 1' > /proc/31861/uid_map > > While this will probably work, the more typical way to do this is with > command(1P). `command' is a shell builtin that will run shell builtins. It only skips shell functions. - -- ``The lyf so short, the craft so long to lerne.'' - Chaucer ``Ars longa, vita brevis'' - Hippocrates Chet Ramey, ITS, CWRUc...@case.eduhttp://cnswww.cns.cwru.edu/~chet/ -BEGIN PGP SIGNATURE- Version: GnuPG v1.4.11 (Darwin) Comment: Using GnuPG with Thunderbird - http://www.enigmail.net/ iEYEARECAAYFAlMx4+QACgkQu1hp8GTqdKt+uACdGGXBCsybrU6qmOXf8g/ibVpX biMAnRAcmljPxqSkHUAAEzuOoIS1mSih =RADZ -END PGP SIGNATURE-
Re: printf cannot write more than one line to /proc/pid/uid_map
Chet Ramey writes: > `command' is a shell builtin that will run shell builtins. It only skips > shell functions. Huh, I guess I have been using zsh for too long. I forgot that the behaviour in bash/POSIX is not the same. pgpYBta6iEqrR.pgp Description: PGP signature
