[SOLVED] how to see process redirects

[lunarul]

Hi,

I am launching a process which redirects output to a file:

wget SOMEURL -O DOWNFILE >LOGFILE 2>&1

I have several processes like this running, and I want to find the LOGFILE corresponding to a certain DOWNFILE. I use

ps aux | grep -r 'wget.*DOWNFILE'

to find the process, but the command column doesn't show the output redirects.

Is there any way to see the output redirects for a given process?

[CSMG Sarma]

Do you mean that how does pipe operator redirect the streams?

[lunarul]

Do you mean that how does pipe operator redirect the streams?

No, I mean that if I launch a command "command >file", then look at the process list with ps, I only see "command". I want to know how to see the ">file".

[CSMG Sarma]

ps prints the command which starts the process you are interested in. It does not keep track of its input or output streams. If you want to see the name of file, you can see it by strace.

With strace you can also see the system calls executed while running you executable with the values passed to them and their return values. This can be handy but equally confusing also. Take care while using it and enjoy debugging!

Hope this was helpful.
Cheers,
Sarma

[lunarul]

I tried strace, but it only showed the write calls, it didn't show what stream the process was writing to.

[CSMG Sarma]

Can you post your program and the strace snapshot?

[lunarul]

Can you post your program and the strace snapshot?

Here's a sample process:

wget URL >test.log 2>&1

After that, from another script, I get the pid using ps and launch:

strace -p 15081

Sample strace output for this:

Process 15081 attached - interrupt to quit
select(5, [4], NULL, NULL, {899, 261722}) = 1 (in [4], left {897, 981109})
read(4, "vAoj\217X\33\246\365\21\0\0$\240A\232\211\25\223\177\311\303\204\237\263H\360(\263\365\245\244\343"..., 16384) = 1340
write(3, "vAoj\217X\33\246\365\21\0\0$\240A\232\211\25\223\177\311\303\204\237\263H\360(\263\365\245\244\343"..., 1340) = 1340
write(2, " "..., 1)                     = 1
write(2, "."..., 1)                     = 1
select(5, [4], NULL, NULL, {900, 0})    = 1 (in [4], left {899, 998986})
read(4, "\341\233\360a5\320\210v\352\230\244M\205{\244\201\241e\202\243A\363\301\4=\242Z>V\373\266\335C"..., 16384) = 1340
write(3, "\341\233\360a5\320\210v\352\230\244M\205{\244\201\241e\202\243A\363\301\4=\242Z>V\373\266\335C"..., 1340) = 1340
write(2, "."..., 1)                     = 1
select(5, [4], NULL, NULL, {900, 0})    = 1 (in [4], left {899, 998486})
read(4, "\347\356\317\352\235<W\201'\267=\317\224`\313\272e#\315J.\1G\274\271\247mU\365\2263\377\244"..., 16384) = 1340
write(3, "\347\356\317\352\235<W\201'\267=\317\224`\313\272e#\315J.\1G\274\271\247mU\365\2263\377\244"..., 1340) = 1340
write(2, "."..., 1)                     = 1
write(2, "."..., 1)                     = 1
select(5, [4], NULL, NULL, {900, 0})    = 1 (in [4], left {899, 964464})
read(4, "6\263\32\270\221\344$\367\320\177\351h\260B-Z\222\261\243\237&kp\346\276F\10m\373\326\270w\334"..., 16384) = 1340
write(3, "6\263\32\270\221\344$\367\320\177\351h\260B-Z\222\261\243\237&kp\346\276F\10m\373\326\270w\334"..., 1340) = 1340
write(2, "."..., 1)                     = 1
select(5, [4], NULL, NULL, {900, 0})    = 1 (in [4], left {899, 998809})
read(4, "\203\32T'\304\3340\222\250h\355\2774\247\325\216\353c\366;$_\300\24s\2052\352\311H\30,\372"..., 16384) = 1340
write(3, "\203\32T'\304\3340\222\250h\355\2774\247\325\216\353c\366;$_\300\24s\2052\352\311H\30,\372"..., 1340) = 1340
write(2, "."..., 1)                     = 1
select(5, [4], NULL, NULL, {900, 0})    = 1 (in [4], left {899, 998745})
read(4, "w\17\6J\21\231\374\316\n|\200'\356\253:x:\254?!\376\276\220\317\324\323;[GQ^\25d"..., 16384) = 1340
write(3, "w\17\6J\21\231\374\316\n|\200'\356\253:x:\254?!\376\276\220\317\324\323;[GQ^\25d"..., 1340) = 1340
write(2, "."..., 1)                     = 1
write(2, "."..., 1)                     = 1
select(5, [4], NULL, NULL, {900, 0})    = 1 (in [4], left {899, 998752})
read(4, "O\203r\311\272\371\33\246\277\3171\302\37\"b\331\224\254\271\243\322$\243\220\335M.\301_\356\7)\275"..., 16384) = 1340
write(3, "O\203r\311\272\371\33\246\277\3171\302\37\"b\331\224\254\271\243\322$\243\220\335M.\301_\356\7)\275"..., 1340) = 1340
write(2, "."..., 1)                     = 1
select(5, [4], NULL, NULL, {900, 0})    = 1 (in [4], left {899, 998494})
Process 15081 detached

No mention of "test.log" in the output.

The thing I'm interested in:
- script A launches wget URL >LOGFILE
- script B knows URL and wants to determine LOGFILE

[lomcevak]

You could use lsof

lsof -p 15081

[lunarul]

You could use lsof

lsof -p 15081

Thanks, that's what I needed.

[liying_gg]

I think if you use ptrace,then you can see the pipe function call.