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Why won't the strings command stop?
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Why won't the strings command stop?
Why is return is ignored during output in bash?Excessively high memory usage reported (3 GB) after reboot&> redirection not working correctlyCentOS can't use new extented space on system discWhy does 'nohup command >& /dev/null' seem to “work” in some shells?Is it bad to have a low entropy in /dev/random?bash - Separate “table” values into strings in arrayWhy stderr is required?0 bytes of swap space available, recommended 10gbDisconnected block device remains in /dev/, sync commands unkillable
The strings command behaves weirdly, apparently it doesn't stop writing to a file even if drive run out of space. Or perhaps I'm missing something?
I run the following:
# strings /dev/urandom > random.txt
this was keep running and didn't stop even after filling the disk (a regular usb flash).
then to be quicker I created a ramdisk and tried again the same command. it also didn't stop.
I understand that urandom isn't a regular file and also strings's output is redirected, however in both cases above, the cat command reported the error when there was no more space.
# cat /dev/urandom > random.txt
cat: write error: No space left on device
- Is this normal behavior of strings? If so, why?
- Where is the data written after there's no more space left?
linux shell string
edited 21 hours ago
Olorin
3,6781621
asked yesterday
user174174user174174
864
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user174174 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
|
show 3 more comments
The strings command behaves weirdly, apparently it doesn't stop writing to a file even if drive run out of space. Or perhaps I'm missing something?
I run the following:
# strings /dev/urandom > random.txt
this was keep running and didn't stop even after filling the disk (a regular usb flash).
then to be quicker I created a ramdisk and tried again the same command. it also didn't stop.
I understand that urandom isn't a regular file and also strings's output is redirected, however in both cases above, the cat command reported the error when there was no more space.
# cat /dev/urandom > random.txt
cat: write error: No space left on device
- Is this normal behavior of strings? If so, why?
- Where is the data written after there's no more space left?
linux shell string
edited 21 hours ago
Olorin
3,6781621
asked yesterday
user174174user174174
864
New contributor
user174174 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
1
What was the indication that your first command had actually filled up the disk?
– Kusalananda
21 hours ago
1
@Kusalananda It was reported by df. I was monitoring it from another virtual terminal using watch df -h
– user174174
21 hours ago
2
@Kusalananda: you can test this easily withstrace strings /dev/urandom > /dev/full
– Peter Cordes
19 hours ago
2
@mosvy OpenBSD uses that samestringsimplementation from GNU binutils. I was referring to thestracecommand.
– Kusalananda
9 hours ago
2
@Kusalananda OK, because the "BSD toolchain" replacement of strings(1) doesn't check for the return value of putchar() either
– mosvy
9 hours ago
|
show 3 more comments
The strings command behaves weirdly, apparently it doesn't stop writing to a file even if drive run out of space. Or perhaps I'm missing something?
I run the following:
# strings /dev/urandom > random.txt
this was keep running and didn't stop even after filling the disk (a regular usb flash).
then to be quicker I created a ramdisk and tried again the same command. it also didn't stop.
I understand that urandom isn't a regular file and also strings's output is redirected, however in both cases above, the cat command reported the error when there was no more space.
# cat /dev/urandom > random.txt
cat: write error: No space left on device
- Is this normal behavior of strings? If so, why?
- Where is the data written after there's no more space left?
linux shell string
edited 21 hours ago
Olorin
3,6781621
asked yesterday
user174174user174174
864
New contributor
user174174 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
The strings command behaves weirdly, apparently it doesn't stop writing to a file even if drive run out of space. Or perhaps I'm missing something?
I run the following:
# strings /dev/urandom > random.txt
this was keep running and didn't stop even after filling the disk (a regular usb flash).
then to be quicker I created a ramdisk and tried again the same command. it also didn't stop.
I understand that urandom isn't a regular file and also strings's output is redirected, however in both cases above, the cat command reported the error when there was no more space.
# cat /dev/urandom > random.txt
cat: write error: No space left on device
- Is this normal behavior of strings? If so, why?
- Where is the data written after there's no more space left?
linux shell string
linux shell string
edited 21 hours ago
Olorin
3,6781621
asked yesterday
user174174user174174
864
New contributor
user174174 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
edited 21 hours ago
Olorin
3,6781621
asked yesterday
user174174user174174
864
New contributor
user174174 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
edited 21 hours ago
Olorin
3,6781621
edited 21 hours ago
Olorin
3,6781621
edited 21 hours ago
Olorin
3,6781621
3,6781621
asked yesterday
user174174user174174
864
New contributor
user174174 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
asked yesterday
user174174user174174
864
asked yesterday
user174174user174174
864
864
New contributor
user174174 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
New contributor
user174174 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
user174174 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
1
What was the indication that your first command had actually filled up the disk?
– Kusalananda
21 hours ago
1
@Kusalananda It was reported by df. I was monitoring it from another virtual terminal using watch df -h
– user174174
21 hours ago
2
@Kusalananda: you can test this easily withstrace strings /dev/urandom > /dev/full
– Peter Cordes
19 hours ago
2
@mosvy OpenBSD uses that samestringsimplementation from GNU binutils. I was referring to thestracecommand.
– Kusalananda
9 hours ago
2
@Kusalananda OK, because the "BSD toolchain" replacement of strings(1) doesn't check for the return value of putchar() either
– mosvy
9 hours ago
|
show 3 more comments
1
What was the indication that your first command had actually filled up the disk?
– Kusalananda
21 hours ago
1
@Kusalananda It was reported by df. I was monitoring it from another virtual terminal using watch df -h
– user174174
21 hours ago
2
@Kusalananda: you can test this easily withstrace strings /dev/urandom > /dev/full
– Peter Cordes
19 hours ago
2
@mosvy OpenBSD uses that samestringsimplementation from GNU binutils. I was referring to thestracecommand.
– Kusalananda
9 hours ago
2
@Kusalananda OK, because the "BSD toolchain" replacement of strings(1) doesn't check for the return value of putchar() either
– mosvy
9 hours ago
1
1
What was the indication that your first command had actually filled up the disk?
– Kusalananda
21 hours ago
What was the indication that your first command had actually filled up the disk?
– Kusalananda
21 hours ago
1
1
@Kusalananda It was reported by df. I was monitoring it from another virtual terminal using watch df -h
– user174174
21 hours ago
@Kusalananda It was reported by df. I was monitoring it from another virtual terminal using watch df -h
– user174174
21 hours ago
2
2
@Kusalananda: you can test this easily with
strace strings /dev/urandom > /dev/full– Peter Cordes
19 hours ago
@Kusalananda: you can test this easily with
strace strings /dev/urandom > /dev/full– Peter Cordes
19 hours ago
2
2
@mosvy OpenBSD uses that same
strings implementation from GNU binutils. I was referring to the strace command.– Kusalananda
9 hours ago
@mosvy OpenBSD uses that same
strings implementation from GNU binutils. I was referring to the strace command.– Kusalananda
9 hours ago
2
2
@Kusalananda OK, because the "BSD toolchain" replacement of strings(1) doesn't check for the return value of putchar() either
– mosvy
9 hours ago
@Kusalananda OK, because the "BSD toolchain" replacement of strings(1) doesn't check for the return value of putchar() either
– mosvy
9 hours ago
|
show 3 more comments
1 Answer
1
active
oldest
votes
If GNU cat can't write out what it read, it will exit with an error:
/* Write this block out. */
/* The following is ok, since we know that 0 < n_read. */
size_t n = n_read;
if (full_write (STDOUT_FILENO, buf, n) != n)
die (EXIT_FAILURE, errno, _("write error"));
GNU strings, on the other hand, doesn't care whether it managed to write successfully:
while (1)
c = get_char (stream, &address, &magiccount, &magic);
if (c == EOF)
break;
if (! STRING_ISGRAPHIC (c))
unget_part_char (c, &address, &magiccount, &magic);
break;
putchar (c);
So all those writes fail, but strings continues merrily along, until it reaches end of input, which will be never.
$ strace -e write strings /dev/urandom > foo/bar
write(1, "7[\Zn]juKwnl [1nTc9gn0&}x(xn/y^7"..., 4096) = 4096
write(1, "nXaki%ndHB0n?5:Qn6bX-np!E[n'&=7n"..., 4096) = 4096
write(1, "%M6sn=4C.%n&7)nnQ_%JncT+";nK*<%n"..., 4096) = 4096
write(1, "&d<nj~g0nm]=ona=^0n%s]2WnM7C%nUK"..., 4096) = -1 ENOSPC (No space left on device)
write(1, "~nd3qQn^^u1#na#5\n^=t"bn*91_n ]o"..., 4096) = -1 ENOSPC (No space left on device)
write(1, "Ln6QO1xna,yEnk>",@ZnyM.urn~ztFnr"..., 4096) = -1 ENOSPC (No space left on device)
write(1, "n61]Rnyg9CnfLVun<Ez:n.tV-cnw_'>e"..., 4096) = -1 ENOSPC (No space left on device)
write(1, "nCj)anT]X:uAn_KH"BnRfQ4Gn3retn&s"..., 4096) = -1 ENOSPC (No space left on device)
write(1, "jnk7@%n9E?^NnJ#8Vn*]i,nXDxh?nr_1"..., 4096) = -1 ENOSPC (No space left on device)
write(1, "iatInQ)ZwnnV0JnE3-W n@0-N2vnK{15"..., 4096) = -1 ENOSPC (No space left on device)
write(1, "nZ~*gn)FQnnUY:GndRbNnn..FnvF
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1 Answer
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1 Answer
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If GNU cat can't write out what it read, it will exit with an error:
/* Write this block out. */
/* The following is ok, since we know that 0 < n_read. */
size_t n = n_read;
if (full_write (STDOUT_FILENO, buf, n) != n)
die (EXIT_FAILURE, errno, _("write error"));
GNU strings, on the other hand, doesn't care whether it managed to write successfully:
while (1)
c = get_char (stream, &address, &magiccount, &magic);
if (c == EOF)
break;
if (! STRING_ISGRAPHIC (c))
unget_part_char (c, &address, &magiccount, &magic);
break;
putchar (c);
So all those writes fail, but strings continues merrily along, until it reaches end of input, which will be never.
$ strace -e write strings /dev/urandom > foo/bar
write(1, "7[\Zn]juKwnl [1nTc9gn0&x(xn/y^7"..., 4096) = 4096
write(1, "nXaki%ndHB0n?5:Qn6bX-np!E[n'&=7n"..., 4096) = 4096
write(1, "%M6sn=4C.%n&7)nnQ_%JncT+";nK*<%n"..., 4096) = 4096
write(1, "&d<nj~g0nm]=ona=^0n%s]2WnM7C%nUK"..., 4096) = -1 ENOSPC (No space left on device)
write(1, "~nd3qQn^^u1#na#5\n^=t"bn*91_n ]o"..., 4096) = -1 ENOSPC (No space left on device)
write(1, "Ln6QO1xna,yEnk>",@ZnyM.urn~ztFnr"..., 4096) = -1 ENOSPC (No space left on device)
write(1, "n61]Rnyg9CnfLVun<Ez:n.tV-cnw_'>e"..., 4096) = -1 ENOSPC (No space left on device)
write(1, "nCj)anT]X:uAn_KH"BnRfQ4Gn3retn&s"..., 4096) = -1 ENOSPC (No space left on device)
write(1, "jnk7@%n9E?^NnJ#8Vn*]i,nXDxh?nr_1"..., 4096) = -1 ENOSPC (No space left on device)
write(1, "iatInQ)ZwnnV0JnE3-W n@0-N2vnK{15"..., 4096) = -1 ENOSPC (No space left on device)
write(1, "nZ~*gn)FQnnUY:GndRbNnn..FnvFimprove this answer
answered 21 hours ago
OlorinOlorin
3,6781621
9
Nice analysis. I'd say that should be considered a bug instrings.
– kasperd
14 hours ago
add a comment x(xn/y^7"..., 4096) = 4096
write(1, "nXaki%ndHB0n?5:Qn6bX-np!E[n'&=7n"..., 4096) = 4096
write(1, "%M6sn=4C.%n&7)nnQ_%JncT+";nK*<%n"..., 4096) = 4096
write(1, "&d<nj~g0nm]=ona=^0n%s]2WnM7C%nUK"..., 4096) = -1 ENOSPC (No space left on device)
write(1, "~nd3qQn^^u1#na#5\n^=t"bn*91_n ]o"..., 4096) = -1 ENOSPC (No space left on device)
write(1, "Ln6QO1xna,yEnk>",@ZnyM.urn~ztFnr"..., 4096) = -1 ENOSPC (No space left on device)
write(1, "n61]Rnyg9CnfLVun<Ez:n.tV-cnw_'>e"..., 4096) = -1 ENOSPC (No space left on device)
write(1, "nCj)anT]X:uAn_KH"BnRfQ4Gn3retn&s"..., 4096) = -1 ENOSPC (No space left on device)
write(1, "jnk7@%n9E?^NnJ#8Vn*]i,nXDxh?nr_1"..., 4096) = -1 ENOSPC (No space left on device)
write(1, "iatInQ)ZwnnV0JnE3-W n@0-N2vnK{15"..., 4096) = -1 ENOSPC (No space left on device)
write(1, "nZ~*gn)FQnnUY:GndRbNnn..FnvFimprove this answer
answered 21 hours ago
OlorinOlorin
3,6781621
9
Nice analysis. I'd say that should be considered a bug instrings.
– kasperd
14 hours ago
add a comment x(xn/y^7"..., 4096) = 4096
write(1, "nXaki%ndHB0n?5:Qn6bX-np!E[n'&=7n"..., 4096) = 4096
write(1, "%M6sn=4C.%n&7)nnQ_%JncT+";nK*<%n"..., 4096) = 4096
write(1, "&d<nj~g0nm]=ona=^0n%s]2WnM7C%nUK"..., 4096) = -1 ENOSPC (No space left on device)
write(1, "~nd3qQn^^u1#na#5\n^=t"bn*91_n ]o"..., 4096) = -1 ENOSPC (No space left on device)
write(1, "Ln6QO1xna,yEnk>",@ZnyM.urn~ztFnr"..., 4096) = -1 ENOSPC (No space left on device)
write(1, "n61]Rnyg9CnfLVun<Ez:n.tV-cnw_'>e"..., 4096) = -1 ENOSPC (No space left on device)
write(1, "nCj)anT]X:uAn_KH"BnRfQ4Gn3retn&s"..., 4096) = -1 ENOSPC (No space left on device)
write(1, "jnk7@%n9E?^NnJ#8Vn*]i,nXDxh?nr_1"..., 4096) = -1 ENOSPC (No space left on device)
write(1, "iatInQ)ZwnnV0JnE3-W n@0-N2vnK{15"..., 4096) = -1 ENOSPC (No space left on device)
write(1, "nZ~*gn)FQnnUY:GndRbNnn..FnvF,n+"..., 4096) = -1 ENOSPC (No space left on device)
...
answered 21 hours ago
OlorinOlorin
3,6781621
answered 21 hours ago
OlorinOlorin
3,6781621
answered 21 hours ago
OlorinOlorin
3,6781621
answered 21 hours ago
OlorinOlorin
3,6781621
3,6781621
9
Nice analysis. I'd say that should be considered a bug instrings.
– kasperd
14 hours ago
add a comment |
9
Nice analysis. I'd say that should be considered a bug instrings.
– kasperd
14 hours ago
9
9
Nice analysis. I'd say that should be considered a bug in
strings.– kasperd
14 hours ago
Nice analysis. I'd say that should be considered a bug in
strings.– kasperd
14 hours ago
add a comment |
user174174 is a new contributor. Be nice, and check out our Code of Conduct.
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user174174 is a new contributor. Be nice, and check out our Code of Conduct.
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1
What was the indication that your first command had actually filled up the disk?
– Kusalananda
21 hours ago
1
@Kusalananda It was reported by df. I was monitoring it from another virtual terminal using watch df -h
– user174174
21 hours ago
2
@Kusalananda: you can test this easily with
strace strings /dev/urandom > /dev/full– Peter Cordes
19 hours ago
2
@mosvy OpenBSD uses that same
stringsimplementation from GNU binutils. I was referring to thestracecommand.– Kusalananda
9 hours ago
2
@Kusalananda OK, because the "BSD toolchain" replacement of strings(1) doesn't check for the return value of putchar() either
– mosvy
9 hours ago