As per the post, which says that[emphasis mine]:
If a process within a background job tries to write to a TTY device, the TTY sends a SIGTTOU signal to the entire job. This will normally suspend the job. It is possible to turn off this feature on a per-TTY basis.
If I understand that statement correctly, there should be no output when invoking ls / & since the ls would receive the SIGTTOU signal when trying to write out, which would suspend the running of ls.
But there is output in the terminal when calling ls /&, which is really out of my expectation.
Here is the output:
ls / &
[1] 75297
jhon#desktop:~$ initrd.img lib32 lost+found opencv_4.0.tar.gz sbin tmp vmlinuz
bin data-ceph data2 etc lfs lib64 media opt root srv usr zeus
boot data.bk dev home lib libx32 mnt proc run sys var
#the cursor twinkles until I hit the enter key.
#empty line
[1]+ Done ls /
jhon#desktop:~$
Am I misunderstanding the aforementioned statement? If I am wrong, please let me know.
What's more, it seems that no SIGTOU signal is ever sent to ls. Here is the output of strace ls / &
strace ls / &
[1] 80908
jhon#desktop::~$ execve("/bin/ls", ["ls", "/"], [/* 29 vars */]) = 0
brk(0) = 0x9d8000
access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory)
access("/etc/ld.so.preload", R_OK) = -1 ENOENT (No such file or directory)
open("/etc/ld.so.cache", O_RDONLY|O_CLOEXEC) = 3
fstat(3, {st_mode=S_IFREG|0644, st_size=122346, ...}) = 0
mmap(NULL, 122346, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7f00e80f2000
close(3) = 0
access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory)
open("/lib/x86_64-linux-gnu/libselinux.so.1", O_RDONLY|O_CLOEXEC) = 3
read(3, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\0[\0\0\0\0\0\0"..., 832) = 832
fstat(3, {st_mode=S_IFREG|0644, st_size=134296, ...}) = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f00e80f1000
mmap(NULL, 2238192, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7f00e7ccb000
mprotect(0x7f00e7ceb000, 2093056, PROT_NONE) = 0
mmap(0x7f00e7eea000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x1f000) = 0x7f00e7eea000
mmap(0x7f00e7eec000, 5872, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x7f00e7eec000
close(3) = 0
access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory)
open("/lib/x86_64-linux-gnu/libacl.so.1", O_RDONLY|O_CLOEXEC) = 3
read(3, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0`\34\0\0\0\0\0\0"..., 832) = 832
fstat(3, {st_mode=S_IFREG|0644, st_size=31168, ...}) = 0
mmap(NULL, 2126336, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7f00e7ac3000
mprotect(0x7f00e7aca000, 2093056, PROT_NONE) = 0
mmap(0x7f00e7cc9000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x6000) = 0x7f00e7cc9000
close(3) = 0
access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory)
open("/lib/x86_64-linux-gnu/libc.so.6", O_RDONLY|O_CLOEXEC) = 3
read(3, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0P \2\0\0\0\0\0"..., 832) = 832
fstat(3, {st_mode=S_IFREG|0755, st_size=1857312, ...}) = 0
mmap(NULL, 3965632, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7f00e76fa000
mprotect(0x7f00e78b8000, 2097152, PROT_NONE) = 0
mmap(0x7f00e7ab8000, 24576, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x1be000) = 0x7f00e7ab8000
mmap(0x7f00e7abe000, 17088, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x7f00e7abe000
close(3) = 0
access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory)
open("/lib/x86_64-linux-gnu/libpcre.so.3", O_RDONLY|O_CLOEXEC) = 3
read(3, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\260\27\0\0\0\0\0\0"..., 832) = 832
fstat(3, {st_mode=S_IFREG|0644, st_size=252032, ...}) = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f00e80f0000
mmap(NULL, 2347200, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7f00e74bc000
mprotect(0x7f00e74f9000, 2093056, PROT_NONE) = 0
mmap(0x7f00e76f8000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x3c000) = 0x7f00e76f8000
close(3) = 0
access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory)
open("/lib/x86_64-linux-gnu/libdl.so.2", O_RDONLY|O_CLOEXEC) = 3
read(3, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\320\16\0\0\0\0\0\0"..., 832) = 832
fstat(3, {st_mode=S_IFREG|0644, st_size=14664, ...}) = 0
mmap(NULL, 2109744, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7f00e72b8000
mprotect(0x7f00e72bb000, 2093056, PROT_NONE) = 0
mmap(0x7f00e74ba000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x2000) = 0x7f00e74ba000
close(3) = 0
access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory)
open("/lib/x86_64-linux-gnu/libattr.so.1", O_RDONLY|O_CLOEXEC) = 3
read(3, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\300\20\0\0\0\0\0\0"..., 832) = 832
fstat(3, {st_mode=S_IFREG|0644, st_size=18624, ...}) = 0
mmap(NULL, 2113760, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7f00e70b3000
mprotect(0x7f00e70b7000, 2093056, PROT_NONE) = 0
mmap(0x7f00e72b6000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x3000) = 0x7f00e72b6000
close(3) = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f00e80ef000
mmap(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f00e80ed000
arch_prctl(ARCH_SET_FS, 0x7f00e80ed840) = 0
mprotect(0x7f00e7ab8000, 16384, PROT_READ) = 0
mprotect(0x7f00e72b6000, 4096, PROT_READ) = 0
mprotect(0x7f00e74ba000, 4096, PROT_READ) = 0
mprotect(0x7f00e76f8000, 4096, PROT_READ) = 0
mprotect(0x7f00e7cc9000, 4096, PROT_READ) = 0
mprotect(0x7f00e7eea000, 4096, PROT_READ) = 0
mprotect(0x619000, 4096, PROT_READ) = 0
mprotect(0x7f00e8110000, 4096, PROT_READ) = 0
munmap(0x7f00e80f2000, 122346) = 0
statfs("/sys/fs/selinux", 0x7ffcbb368ce0) = -1 ENOENT (No such file or directory)
statfs("/selinux", 0x7ffcbb368ce0) = -1 ENOENT (No such file or directory)
brk(0) = 0x9d8000
brk(0x9f9000) = 0x9f9000
open("/proc/filesystems", O_RDONLY) = 3
fstat(3, {st_mode=S_IFREG|0444, st_size=0, ...}) = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f00e810f000
read(3, "nodev\tsysfs\nnodev\trootfs\nnodev\tr"..., 1024) = 400
read(3, "", 1024) = 0
close(3) = 0
munmap(0x7f00e810f000, 4096) = 0
ioctl(1, SNDCTL_TMR_TIMEBASE or SNDRV_TIMER_IOCTL_NEXT_DEVICE or TCGETS, {B38400 opost isig -icanon -echo ...}) = 0
ioctl(1, TIOCGWINSZ, {ws_row=35, ws_col=169, ws_xpixel=169, ws_ypixel=35}) = 0
stat("/", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
openat(AT_FDCWD, "/", O_RDONLY|O_NONBLOCK|O_DIRECTORY|O_CLOEXEC) = 3
getdents(3, /* 38 entries */, 32768) = 1080
getdents(3, /* 0 entries */, 32768) = 0
close(3) = 0
fstat(1, {st_mode=S_IFCHR|0620, st_rdev=makedev(136, 89), ...}) = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f00e810f000
write(1, "VCAST_GUI_SIZES.plist data\t da"..., 140VCAST_GUI_SIZES.plist data data1 dms_windows_server initrd.img lib32 lost+found opencv_4.0.tar.gz reportlog.log sbin tmp vmlinuz
) = 140
write(1, "bin\t\t data-ceph data2 et"..., 96bin data-ceph data2 etc lfs lib64 media opt root srv usr zeus
) = 96
write(1, "boot\t\t data.bk\t dev\t home"..., 88boot data.bk dev home lib libx32 mnt proc run sys var
) = 88
close(1) = 0
munmap(0x7f00e810f000, 4096) = 0
close(2) = 0
exit_group(0) = ?
+++ exited with 0 +++
[1]+ Done strace ls /
I'm attempting to print to standard out from the following Perl script, but it doesn't produce any output on the screen. It does print to a file, however.
#!/usr/bin/perl
use warnings;
use strict;
print "Here's some text\n";
print STDERR "Here's some text\n";
print STDOUT "Here's some text\n";
open FH, ">", "file.txt" or die $!;
print FH "Here's some text\n";
I tried checking the version of perl I'm using (perl -v), but that doesn't output anything either. The perl man page tells me I'm using 5.14.2. I'm running the Perl script from a bash prompt from a Raspberry Pi.
I saw this similar post Print: producing no output, so I used strace and saw that the output did not include any write commands.
strace perl -we'print("a") or die("Can'\''t print: $!\n");'
Here's the strace output for the full script:
execve("./response", ["./response"], [/* 18 vars */]) = 0
brk(0) = 0xd98000
uname({sys="Linux", node="raspberrypi", ...}) = 0
access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory)
mmap2(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb6f99000
access("/etc/ld.so.preload", R_OK) = 0
open("/etc/ld.so.preload", O_RDONLY) = 3
fstat64(3, {st_mode=S_IFREG|0644, st_size=44, ...}) = 0
mmap2(NULL, 44, PROT_READ|PROT_WRITE, MAP_PRIVATE, 3, 0) = 0xb6f98000
close(3) = 0
open("/usr/lib/arm-linux-gnueabihf/libcofi_rpi.so", O_RDONLY) = 3
read(3, "\177ELF\1\1\1\0\0\0\0\0\0\0\0\0\3\0(\0\1\0\0\0\270\4\0\0004\0\0\0"..., 512) = 512
lseek(3, 7276, SEEK_SET) = 7276
read(3, "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 1080) = 1080
lseek(3, 7001, SEEK_SET) = 7001
read(3, "A.\0\0\0aeabi\0\1$\0\0\0\0056\0\6\6\10\1\t\1\n\2\22\4\24\1\25"..., 47) = 47
fstat64(3, {st_mode=S_IFREG|0755, st_size=10170, ...}) = 0
mmap2(NULL, 39740, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0xb6f6c000
mprotect(0xb6f6e000, 28672, PROT_NONE) = 0
mmap2(0xb6f75000, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x1) = 0xb6f75000
close(3) = 0
munmap(0xb6f98000, 44) = 0
open("/etc/ld.so.cache", O_RDONLY) = 3
fstat64(3, {st_mode=S_IFREG|0644, st_size=64456, ...}) = 0
mmap2(NULL, 64456, PROT_READ, MAP_PRIVATE, 3, 0) = 0xb6f5c000
close(3) = 0
access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory)
open("/usr/lib/libperl.so.5.14", O_RDONLY) = 3
read(3, "\177ELF\1\1\1\0\0\0\0\0\0\0\0\0\3\0(\0\1\0\0\0\220\v\2\0004\0\0\0"..., 512) = 512
lseek(3, 1346508, SEEK_SET) = 1346508
read(3, "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 1120) = 1120
lseek(3, 1346184, SEEK_SET) = 1346184
read(3, "A2\0\0\0aeabi\0\1(\0\0\0\0056\0\6\6\10\1\t\1\n\2\22\4\24\1\25"..., 51) = 51
fstat64(3, {st_mode=S_IFREG|0644, st_size=1347628, ...}) = 0
mmap2(NULL, 1379192, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0xb6e0b000
mprotect(0xb6f4f000, 32768, PROT_NONE) = 0
mmap2(0xb6f57000, 20480, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x144) = 0xb6f57000
close(3) = 0
access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory)
open("/lib/arm-linux-gnueabihf/libdl.so.2", O_RDONLY) = 3
read(3, "\177ELF\1\1\1\0\0\0\0\0\0\0\0\0\3\0(\0\1\0\0\0(\t\0\0004\0\0\0"..., 512) = 512
lseek(3, 8652, SEEK_SET) = 8652
read(3, "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 1160) = 1160
lseek(3, 8320, SEEK_SET) = 8320
read(3, "A0\0\0\0aeabi\0\1&\0\0\0\0056\0\6\6\10\1\t\1\n\2\22\4\24\1\25"..., 49) = 49
fstat64(3, {st_mode=S_IFREG|0644, st_size=9812, ...}) = 0
mmap2(NULL, 41136, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0xb6e00000
mprotect(0xb6e02000, 28672, PROT_NONE) = 0
mmap2(0xb6e09000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x1) = 0xb6e09000
close(3) = 0
access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory)
open("/lib/arm-linux-gnueabihf/libm.so.6", O_RDONLY) = 3
read(3, "\177ELF\1\1\1\0\0\0\0\0\0\0\0\0\3\0(\0\1\0\0\0\3201\0\0004\0\0\0"..., 512) = 512
lseek(3, 426468, SEEK_SET) = 426468
read(3, "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 1160) = 1160
lseek(3, 426136, SEEK_SET) = 426136
read(3, "A0\0\0\0aeabi\0\1&\0\0\0\0056\0\6\6\10\1\t\1\n\2\22\4\24\1\25"..., 49) = 49
fstat64(3, {st_mode=S_IFREG|0644, st_size=427628, ...}) = 0
mmap2(NULL, 458912, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0xb6d8f000
mprotect(0xb6df7000, 28672, PROT_NONE) = 0
mmap2(0xb6dfe000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x67) = 0xb6dfe000
close(3) = 0
access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory)
open("/lib/arm-linux-gnueabihf/libpthread.so.0", O_RDONLY) = 3
read(3, "\177ELF\1\1\1\0\0\0\0\0\0\0\0\0\3\0(\0\1\0\0\0\274V\0\0004\0\0\0"..., 512) = 512
lseek(3, 82712, SEEK_SET) = 82712
read(3, "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 1400) = 1400
lseek(3, 82308, SEEK_SET) = 82308
read(3, "A0\0\0\0aeabi\0\1&\0\0\0\0056\0\6\6\10\1\t\1\n\2\22\4\24\1\25"..., 49) = 49
fstat64(3, {st_mode=S_IFREG|0755, st_size=116462, ...}) = 0
mmap2(NULL, 123412, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0xb6d70000
mprotect(0xb6d84000, 28672, PROT_NONE) = 0
mmap2(0xb6d8b000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x13) = 0xb6d8b000
mmap2(0xb6d8d000, 4628, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0xb6d8d000
close(3) = 0
access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory)
open("/lib/arm-linux-gnueabihf/libc.so.6", O_RDONLY) = 3
read(3, "\177ELF\1\1\1\0\0\0\0\0\0\0\0\0\3\0(\0\1\0\0\0\214y\1\0004\0\0\0"..., 512) = 512
lseek(3, 1215264, SEEK_SET) = 1215264
read(3, "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 1360) = 1360
lseek(3, 1214828, SEEK_SET) = 1214828
read(3, "A.\0\0\0aeabi\0\1$\0\0\0\0056\0\6\6\10\1\t\1\n\2\22\4\24\1\25"..., 47) = 47
fstat64(3, {st_mode=S_IFREG|0755, st_size=1216624, ...}) = 0
mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb6f98000
mmap2(NULL, 1258784, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0xb6c3c000
mprotect(0xb6d62000, 32768, PROT_NONE) = 0
mmap2(0xb6d6a000, 12288, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x126) = 0xb6d6a000
mmap2(0xb6d6d000, 9504, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0xb6d6d000
close(3) = 0
access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory)
open("/lib/arm-linux-gnueabihf/libcrypt.so.1", O_RDONLY) = 3
read(3, "\177ELF\1\1\1\0\0\0\0\0\0\0\0\0\3\0(\0\1\0\0\0\30\7\0\0004\0\0\0"..., 512) = 512
lseek(3, 29116, SEEK_SET) = 29116
read(3, "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 1160) = 1160
lseek(3, 28780, SEEK_SET) = 28780
read(3, "A0\0\0\0aeabi\0\1&\0\0\0\0056\0\6\6\10\1\t\1\n\2\22\4\24\1\25"..., 49) = 49
fstat64(3, {st_mode=S_IFREG|0644, st_size=30276, ...}) = 0
mmap2(NULL, 221504, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0xb6c05000
mprotect(0xb6c0c000, 28672, PROT_NONE) = 0
mmap2(0xb6c13000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x6) = 0xb6c13000
mmap2(0xb6c15000, 155968, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0xb6c15000
close(3) = 0
access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory)
open("/lib/arm-linux-gnueabihf/libgcc_s.so.1", O_RDONLY) = 3
read(3, "\177ELF\1\1\1\0\0\0\0\0\0\0\0\0\3\0(\0\1\0\0\0`\364\0\0004\0\0\0"..., 512) = 512
lseek(3, 130212, SEEK_SET) = 130212
read(3, "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 1160) = 1160
lseek(3, 129880, SEEK_SET) = 129880
read(3, "A2\0\0\0aeabi\0\1(\0\0\0\0056\0\6\6\10\1\t\1\n\2\22\4\24\1\25"..., 51) = 51
fstat64(3, {st_mode=S_IFREG|0644, st_size=131372, ...}) = 0
mmap2(NULL, 162704, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0xb6bdd000
mprotect(0xb6bfd000, 28672, PROT_NONE) = 0
mmap2(0xb6c04000, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x1f) = 0xb6c04000
close(3) = 0
mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb6f97000
set_tls(0xb6f976d0, 0xb6f97da8, 0xb6f9c048, 0xb6f976d0, 0xb6f9c048) = 0
mprotect(0xb6c13000, 4096, PROT_READ) = 0
mprotect(0xb6d6a000, 8192, PROT_READ) = 0
mprotect(0xb6d8b000, 4096, PROT_READ) = 0
mprotect(0xb6dfe000, 4096, PROT_READ) = 0
mprotect(0xb6e09000, 4096, PROT_READ) = 0
mprotect(0xb6f57000, 8192, PROT_READ) = 0
mprotect(0x11000, 4096, PROT_READ) = 0
mprotect(0xb6f9b000, 4096, PROT_READ) = 0
munmap(0xb6f5c000, 64456) = 0
set_tid_address(0xb6f97278) = 12607
set_robust_list(0xb6f97280, 0xc) = 0
futex(0xbece6778, FUTEX_WAIT_BITSET_PRIVATE|FUTEX_CLOCK_REALTIME, 1, NULL, b6d8c000) = -1 EAGAIN (Resource temporarily unavailable)
rt_sigaction(SIGRTMIN, {0xb6d7520c, [], SA_SIGINFO|0x4000000}, NULL, 8) = 0
rt_sigaction(SIGRT_1, {0xb6d750b4, [], SA_RESTART|SA_SIGINFO|0x4000000}, NULL, 8) = 0
rt_sigprocmask(SIG_UNBLOCK, [RTMIN RT_1], NULL, 8) = 0
getrlimit(RLIMIT_STACK, {rlim_cur=8192*1024, rlim_max=RLIM_INFINITY}) = 0
rt_sigaction(SIGFPE, {SIG_IGN, [FPE], SA_RESTART|0x4000000}, {SIG_DFL, [], 0}, 8) = 0
brk(0) = 0xd98000
brk(0xdb9000) = 0xdb9000
getuid32() = 1001
geteuid32() = 1001
getgid32() = 1004
getegid32() = 1004
open("/usr/lib/locale/locale-archive", O_RDONLY|O_LARGEFILE) = 3
fstat64(3, {st_mode=S_IFREG|0644, st_size=1534656, ...}) = 0
mmap2(NULL, 1534656, PROT_READ, MAP_PRIVATE, 3, 0) = 0xb6a66000
close(3) = 0
open("/dev/urandom", O_RDONLY|O_LARGEFILE) = 3
read(3, "~\210\223\234", 4) = 4
close(3) = 0
gettimeofday({1460938704, 307768}, NULL) = 0
readlink("/proc/self/exe", "/usr/bin/perl", 4095) = 13
stat64("/usr/local/lib/site_perl/5.14.2/arm-linux-gnueabihf-thread-multi-64int", 0xbece6368) = -1 ENOENT (No such file or directory)
stat64("/usr/local/lib/site_perl/5.14.2", 0xbece6368) = -1 ENOENT (No such file or directory)
stat64("/usr/local/lib/site_perl/arm-linux-gnueabihf-thread-multi-64int", 0xbece6368) = -1 ENOENT (No such file or directory)
open("./response", O_RDONLY|O_LARGEFILE) = 3
ioctl(3, SNDCTL_TMR_TIMEBASE or TCGETS, 0xbece627c) = -1 ENOTTY (Inappropriate ioctl for device)
_llseek(3, 0, [0], SEEK_CUR) = 0
fcntl64(3, F_SETFD, FD_CLOEXEC) = 0
rt_sigaction(SIGCHLD, NULL, {SIG_DFL, [], 0}, 8) = 0
brk(0xddb000) = 0xddb000
read(3, "#!/usr/bin/perl\nuse warnings;\nus"..., 8192) = 210
stat64("/etc/perl/warnings.pmc", 0xbece5e10) = -1 ENOENT (No such file or directory)
stat64("/etc/perl/warnings.pm", 0xbece5d90) = -1 ENOENT (No such file or directory)
stat64("/usr/local/lib/perl/5.14.2/warnings.pmc", 0xbece5e10) = -1 ENOENT (No such file or directory)
stat64("/usr/local/lib/perl/5.14.2/warnings.pm", 0xbece5d90) = -1 ENOENT (No such file or directory)
stat64("/usr/local/share/perl/5.14.2/warnings.pmc", 0xbece5e10) = -1 ENOENT (No such file or directory)
stat64("/usr/local/share/perl/5.14.2/warnings.pm", 0xbece5d90) = -1 ENOENT (No such file or directory)
stat64("/usr/lib/perl5/warnings.pmc", 0xbece5e10) = -1 ENOENT (No such file or directory)
stat64("/usr/lib/perl5/warnings.pm", 0xbece5d90) = -1 ENOENT (No such file or directory)
stat64("/usr/share/perl5/warnings.pmc", 0xbece5e10) = -1 ENOENT (No such file or directory)
stat64("/usr/share/perl5/warnings.pm", 0xbece5d90) = -1 ENOENT (No such file or directory)
stat64("/usr/lib/perl/5.14/warnings.pmc", 0xbece5e10) = -1 ENOENT (No such file or directory)
stat64("/usr/lib/perl/5.14/warnings.pm", 0xbece5d90) = -1 ENOENT (No such file or directory)
stat64("/usr/share/perl/5.14/warnings.pmc", 0xbece5e10) = -1 ENOENT (No such file or directory)
stat64("/usr/share/perl/5.14/warnings.pm", {st_mode=S_IFREG|0644, st_size=15015, ...}) = 0
open("/usr/share/perl/5.14/warnings.pm", O_RDONLY|O_LARGEFILE) = 4
ioctl(4, SNDCTL_TMR_TIMEBASE or TCGETS, 0xbece5be4) = -1 ENOTTY (Inappropriate ioctl for device)
_llseek(4, 0, [0], SEEK_CUR) = 0
read(4, "# -*- buffer-read-only: t -*-\n# "..., 8192) = 8192
read(4, "08\\x00\\x00\\x00\\x00\\x00\\x00\\x00\\x"..., 8192) = 6823
read(4, "", 8192) = 0
close(4) = 0
brk(0xdfc000) = 0xdfc000
stat64("/etc/perl/strict.pmc", 0xbece5e10) = -1 ENOENT (No such file or directory)
stat64("/etc/perl/strict.pm", 0xbece5d90) = -1 ENOENT (No such file or directory)
stat64("/usr/local/lib/perl/5.14.2/strict.pmc", 0xbece5e10) = -1 ENOENT (No such file or directory)
stat64("/usr/local/lib/perl/5.14.2/strict.pm", 0xbece5d90) = -1 ENOENT (No such file or directory)
stat64("/usr/local/share/perl/5.14.2/strict.pmc", 0xbece5e10) = -1 ENOENT (No such file or directory)
stat64("/usr/local/share/perl/5.14.2/strict.pm", 0xbece5d90) = -1 ENOENT (No such file or directory)
stat64("/usr/lib/perl5/strict.pmc", 0xbece5e10) = -1 ENOENT (No such file or directory)
stat64("/usr/lib/perl5/strict.pm", 0xbece5d90) = -1 ENOENT (No such file or directory)
stat64("/usr/share/perl5/strict.pmc", 0xbece5e10) = -1 ENOENT (No such file or directory)
stat64("/usr/share/perl5/strict.pm", 0xbece5d90) = -1 ENOENT (No such file or directory)
stat64("/usr/lib/perl/5.14/strict.pmc", 0xbece5e10) = -1 ENOENT (No such file or directory)
stat64("/usr/lib/perl/5.14/strict.pm", 0xbece5d90) = -1 ENOENT (No such file or directory)
stat64("/usr/share/perl/5.14/strict.pmc", 0xbece5e10) = -1 ENOENT (No such file or directory)
stat64("/usr/share/perl/5.14/strict.pm", {st_mode=S_IFREG|0644, st_size=879, ...}) = 0
open("/usr/share/perl/5.14/strict.pm", O_RDONLY|O_LARGEFILE) = 4
ioctl(4, SNDCTL_TMR_TIMEBASE or TCGETS, 0xbece5be4) = -1 ENOTTY (Inappropriate ioctl for device)
_llseek(4, 0, [0], SEEK_CUR) = 0
read(4, "package strict;\n\n$strict::VERSIO"..., 8192) = 879
_llseek(4, 878, [878], SEEK_SET) = 0
_llseek(4, 0, [878], SEEK_CUR) = 0
close(4) = 0
read(3, "", 8192) = 0
open("file.txt", O_WRONLY|O_CREAT|O_TRUNC|O_LARGEFILE, 0666) = 4
ioctl(4, SNDCTL_TMR_TIMEBASE or TCGETS, 0xbece614c) = -1 ENOTTY (Inappropriate ioctl for device)
_llseek(4, 0, [0], SEEK_CUR) = 0
fstat64(4, {st_mode=S_IFREG|0644, st_size=0, ...}) = 0
fcntl64(4, F_SETFD, FD_CLOEXEC) = 0
rt_sigaction(SIG_0, NULL, {0xb6e18dc4, [TRAP RTMIN RT_1 RT_2 RT_3 RT_12 RT_13 RT_15 RT_16 RT_18 RT_19 RT_20 RT_25 RT_26 RT_27 RT_28 RT_29], SA_SIGINFO|0x85b8}, 8) = -1 EINVAL (Invalid argument)
rt_sigaction(SIGHUP, NULL, {SIG_DFL, [], 0}, 8) = 0
rt_sigaction(SIGINT, NULL, {SIG_DFL, [], 0}, 8) = 0
rt_sigaction(SIGQUIT, NULL, {SIG_DFL, [], 0}, 8) = 0
rt_sigaction(SIGILL, NULL, {SIG_DFL, [], 0}, 8) = 0
rt_sigaction(SIGTRAP, NULL, {SIG_DFL, [], 0}, 8) = 0
rt_sigaction(SIGABRT, NULL, {SIG_DFL, [], 0}, 8) = 0
rt_sigaction(SIGBUS, NULL, {SIG_DFL, [], 0}, 8) = 0
rt_sigaction(SIGFPE, NULL, {SIG_IGN, [FPE], SA_RESTART|0x4000000}, 8) = 0
rt_sigaction(SIGKILL, NULL, {SIG_DFL, [], 0}, 8) = 0
rt_sigaction(SIGUSR1, NULL, {SIG_DFL, [], 0}, 8) = 0
rt_sigaction(SIGSEGV, NULL, {SIG_DFL, [], 0}, 8) = 0
rt_sigaction(SIGUSR2, NULL, {SIG_DFL, [], 0}, 8) = 0
rt_sigaction(SIGPIPE, NULL, {SIG_DFL, [], 0}, 8) = 0
rt_sigaction(SIGALRM, NULL, {SIG_DFL, [], 0}, 8) = 0
rt_sigaction(SIGTERM, NULL, {SIG_DFL, [], 0}, 8) = 0
rt_sigaction(SIGSTKFLT, NULL, {SIG_DFL, [], 0}, 8) = 0
rt_sigaction(SIGCHLD, NULL, {SIG_DFL, [], 0}, 8) = 0
rt_sigaction(SIGCONT, NULL, {SIG_DFL, [], 0}, 8) = 0
rt_sigaction(SIGSTOP, NULL, {SIG_DFL, [], 0}, 8) = 0
rt_sigaction(SIGTSTP, NULL, {SIG_DFL, [], 0}, 8) = 0
rt_sigaction(SIGTTIN, NULL, {SIG_DFL, [], 0}, 8) = 0
rt_sigaction(SIGTTOU, NULL, {SIG_DFL, [], 0}, 8) = 0
rt_sigaction(SIGURG, NULL, {SIG_DFL, [], 0}, 8) = 0
rt_sigaction(SIGXCPU, NULL, {SIG_DFL, [], 0}, 8) = 0
rt_sigaction(SIGXFSZ, NULL, {SIG_DFL, [], 0}, 8) = 0
rt_sigaction(SIGVTALRM, NULL, {SIG_DFL, [], 0}, 8) = 0
rt_sigaction(SIGPROF, NULL, {SIG_DFL, [], 0}, 8) = 0
rt_sigaction(SIGWINCH, NULL, {SIG_DFL, [], 0}, 8) = 0
rt_sigaction(SIGIO, NULL, {SIG_DFL, [], 0}, 8) = 0
rt_sigaction(SIGPWR, NULL, {SIG_DFL, [], 0}, 8) = 0
rt_sigaction(SIGSYS, NULL, {SIG_DFL, [], 0}, 8) = 0
rt_sigaction(SIGRT_2, NULL, {SIG_DFL, [], 0}, 8) = 0
rt_sigaction(SIGRT_3, NULL, {SIG_DFL, [], 0}, 8) = 0
rt_sigaction(SIGRT_4, NULL, {SIG_DFL, [], 0}, 8) = 0
rt_sigaction(SIGRT_5, NULL, {SIG_DFL, [], 0}, 8) = 0
rt_sigaction(SIGRT_6, NULL, {SIG_DFL, [], 0}, 8) = 0
rt_sigaction(SIGRT_7, NULL, {SIG_DFL, [], 0}, 8) = 0
rt_sigaction(SIGRT_8, NULL, {SIG_DFL, [], 0}, 8) = 0
rt_sigaction(SIGRT_9, NULL, {SIG_DFL, [], 0}, 8) = 0
rt_sigaction(SIGRT_10, NULL, {SIG_DFL, [], 0}, 8) = 0
rt_sigaction(SIGRT_11, NULL, {SIG_DFL, [], 0}, 8) = 0
rt_sigaction(SIGRT_12, NULL, {SIG_DFL, [], 0}, 8) = 0
rt_sigaction(SIGRT_13, NULL, {SIG_DFL, [], 0}, 8) = 0
rt_sigaction(SIGRT_14, NULL, {SIG_DFL, [], 0}, 8) = 0
rt_sigaction(SIGRT_15, NULL, {SIG_DFL, [], 0}, 8) = 0
rt_sigaction(SIGRT_16, NULL, {SIG_DFL, [], 0}, 8) = 0
rt_sigaction(SIGRT_17, NULL, {SIG_DFL, [], 0}, 8) = 0
rt_sigaction(SIGRT_18, NULL, {SIG_DFL, [], 0}, 8) = 0
rt_sigaction(SIGRT_19, NULL, {SIG_DFL, [], 0}, 8) = 0
rt_sigaction(SIGRT_20, NULL, {SIG_DFL, [], 0}, 8) = 0
rt_sigaction(SIGRT_21, NULL, {SIG_DFL, [], 0}, 8) = 0
rt_sigaction(SIGRT_22, NULL, {SIG_DFL, [], 0}, 8) = 0
rt_sigaction(SIGRT_23, NULL, {SIG_DFL, [], 0}, 8) = 0
rt_sigaction(SIGRT_24, NULL, {SIG_DFL, [], 0}, 8) = 0
rt_sigaction(SIGRT_25, NULL, {SIG_DFL, [], 0}, 8) = 0
rt_sigaction(SIGRT_26, NULL, {SIG_DFL, [], 0}, 8) = 0
rt_sigaction(SIGRT_27, NULL, {SIG_DFL, [], 0}, 8) = 0
rt_sigaction(SIGRT_28, NULL, {SIG_DFL, [], 0}, 8) = 0
rt_sigaction(SIGRT_29, NULL, {SIG_DFL, [], 0}, 8) = 0
rt_sigaction(SIGRT_30, NULL, {SIG_DFL, [], 0}, 8) = 0
rt_sigaction(SIGRT_31, NULL, {SIG_DFL, [], 0}, 8) = 0
rt_sigaction(SIGRT_32, NULL, {SIG_DFL, [], 0}, 8) = 0
rt_sigaction(SIGABRT, NULL, {SIG_DFL, [], 0}, 8) = 0
rt_sigaction(SIGCHLD, NULL, {SIG_DFL, [], 0}, 8) = 0
rt_sigaction(SIGIO, NULL, {SIG_DFL, [], 0}, 8) = 0
rt_sigaction(SIGSYS, NULL, {SIG_DFL, [], 0}, 8) = 0
write(4, "Here's some text\n", 17) = 17
close(4) = 0
close(3) = 0
exit_group(0) = ?
Any ideas about why it's not producing output? A bash script can echo text to standard out just fine.
When I run the script in debug mode it does print output.
After executing perl -v at the command line the exit code from $? was 0.
Executing
perl -e'print "foo" or die $!'
gave and exit code of 9, but that appears to be due to the die. perl -v > file did not write anything to file.
Here is the output of stat STDOUT and the command used to write it to a file:
45826|261126|33188|1|1001|1004|0|0|1461024408|1461035504|1461035504|4096|0
perl -e 'open my $FH, ">file"; print $FH join "|", stat STDOUT '
Before starting reading have a look at the output of this command. Everything is pointing to STDOUT pointing to the incorrect place.
ls -l /proc/$$/fd/{1,2}
On my system I get this, note it does change as I write this because this was not written in one go.
lrwx------ 1 root root 64 May 3 17:01 /proc/27806/fd/1 -> /dev/pts/1
lrwx------ 1 root root 64 May 3 17:01 /proc/27806/fd/2 -> /dev/pts/1
I suspect the above to be similar for you. The stat looks suspicious to me, if I had access to the filesytem I'd search for the inode that it's telling me its writing to ie.
sudo find / -printf "%i:\t%p\n"|grep 261126
If when Perl starts it's changing it's stdout etc to the wrong place I'd add a very long sleep to the script then do the search to see where it is. If the file is a regular file and it's on the filesystem this should find it.
My stat on STDOUT
|dev |inode |mode |link |uid |gid |rdev |size |atime |mtime |ctime |blk |blka
|13 |3 |8592 |1 |1000|5 |34816|0 |1462301986|1462301986|1462301958|1024|0
Your stat on STDOUT
|dev |inode |mode |link |uid |gid |rdev |size |atime |mtime |ctime |blk |blka
|45826 |261126 |33188 |1 |1001|1004|0 |0 |1461024408|1461035504|1461035504|4096|0
On mine my dev has minor number 13 and looks ok when I search for it under devices. If we mask yours off to show major/minor you have...
major == 179
minor == 2
Note, I originally had these in reverse until corrected by Wumpus Q. Wumbley.
On my machine this is
crw------- 1 root root 2, 179 Apr 29 12:50 ptya3
On mine my rdev equates to
major == 136
minor == 0
On my Debian system this is /dev/pts/0. Your rdev is 0. I had a quick look round and some people using screen can have problems with /dev/pts/N ie it's not there but that's me guessing.
The strace is also really odd, I got the following lines when it wrote on my system:
read(3, "#!/usr/bin/perl -w\n#use strict;\n"..., 8192) = 228
read(3, "", 8192) = 0
close(3) = 0
write(1, "Here's some text STDOUT\n", 24Here's some text STDOUT
) = 24
write(2, "Here's some text STDERR\n", 24Here's some text STDERR
) = 24
write(1, "Here's some text STDOUT\n", 24Here's some text STDOUT
) = 24
The fact that these appear no where in your strace is very strange indeed. You can change where the appear by messing around with $| but they should appear somewhere. Gilles noticed that the mode is also odd. If you run this script...
#!/usr/bin/perl
use warnings;
use strict;
use Fcntl ':mode';
my $mode = 33188;
my $user_rwx = ($mode & S_IRWXU) >> 6;
print("user_rwx = $user_rwx\n");
my $group_read = ($mode & S_IRGRP) >> 3;
print("group_read = $group_read\n");
my $other_execute = $mode & S_IXOTH;
print("other_execute = $other_execute\n");
printf "Permissions are %04o\n", S_IMODE($mode), "\n";
my $is_setuid = $mode & S_ISUID;
print("is_setuid = $is_setuid\n");
my $is_directory = S_ISDIR($mode);
print("dir = $is_directory\n");
my $is_reg = S_ISREG($mode);
print("regular = $is_reg\n");
You can see that STDOUT appears to be pointing at a regular file. This would confirm why rdev is zero ie if stdout was redirecting to something that was meant to be a device but actually was just a normal file. I've seen odd things like that happen in chrooted environments where devices were not setup properly.
Regardless of buffering being on or off on exit the buffers should have have been flushed ie you would see calls to the write sys call. It's really weird that there are no writes at all in the strace.
There are several interesting clues in the information you've provided:
perl -e'print "foo" or die $!' gave an exit code of 9, which is EBADF, implying that STDOUT is pointing to a bad file descriptor. That could either be some arbitrary number (since the underlying file descriptors are just numbers), or it could be a file descriptor which used to be open but is now closed. (That also implies that it's not, say, redirected to /dev/null -- that would result in no output but wouldn't give an error.)
Your strace output shows several open and close calls, and they all appear to be paired--no evidence of closing STDOUT. Importantly, the open calls all return FD 3 (and later, FD 4 in a case in which FD 3 is still in use)--on Unix-like systems, open typically returns the lowest unused FD, so this is further evidence that FD 1 (the usual STDOUT) hasn't been closed after your process started.
So the implications is that STDOUT is not connected to FD 1, but is associated with some other FD. Running the following should tell you what FD it is:
perl -e 'open my $FH, ">", file.txt"; print $FH fileno(STDOUT)'
I'm guessing that this will be some arbitrary number, and the result of some problem specific to your installation on your Raspberry Pi--perhaps some corrupt library. But as suggested by Sebastian, you can run lsof to find out what FDs your process has opened (add a sleep to your script to keep it running), or look in /proc. But probably STDOUT is referring to something that isn't actually an open FD. It's a little curious that your strace output doesn't show even error-ing calls to write; that implies that Perl does know that the FD is invalid.
Another interesting experiment to try is running this:
perl -e 'system qw(echo hello)'
If that produces output, then that means that the subprocess is inheriting a still-open FD 1, which is further evidence that Perl is in a bad state and has STDOUT associated with an unexpected FD.
Yet another thing to try is this:
perl -le 'open(STDOUT, ">&1"); print "hello"'
That's an attempt to "fix" STDOUT by re-opening it with an FD dup2()'d from FD 1 (which I'm inferring is still open, and just not associated with STDOUT). If that produces output, then at least it's a possible workaround, though still not an explanation of the original cause (which I fear will remain inscrutable).
One side note: Although perl -V isn't giving you any output, you can get the information by running:
perl -MConfig -le 'open my $FH, ">", version.txt"; print Config::myconfig(); print foreach Config::local_patches()'
The second part, about locally-applied patches, may give a clue as to whether something non-standard was done to the perl you have installed.
Try making a fresh user account and using that to see if the same issue occurs, i would also try it on a newer Perl because i can't reproduce this on a pi that has 5.22 on it. This seems very much like you have something unexpected in your shell, a broken module installation or you have a mysterious prompt command that is gobbling output.
The lack of writes to STDOUT and STDERR in your strace suggests they were somehow opened the wrong way before that part of the code ran.
Try adding $|=1 after your use lines:
#!/usr/bin/perl
use warnings;
use strict;
$|=1;
print "Here's some text\n";
print STDERR "Here's some text\n";
print STDOUT "Here's some text\n";
open FH, ">", "file.txt" or die $!;
print FH "Here's some text\n";
Your strace output also shows that the print-to-file is done at script exit, not while the script is running, because of Perl's output buffering.
If the $|=1 doesn't help: Try getting the FDs used by your script:
#!/usr/bin/perl
system "ls -l /proc/$$/fd";
or
#!/usr/bin/perl
system "lsof -p $$";
They should give you a hint where the output should go.
I want to understand how does memory leak checkers identify if a free has been called for a given malloc.
malloc can easily be identified by brk system calls, so if i am writing a profiler and do a single stepping on a process which breaks at system calls i can easily understand that malloc has been done.
How can i find if a free has been called for this malloc?
Below is the output from strace. This code has free, how can we tell if free was invoked by checking this strace -
read(0, "13608\n", 4096) = 6
brk(0) = 0x8cc6000
brk(0x8ce7000) = 0x8ce7000
write(1, "File name - /proc/13608/maps\n", 29) = 29
open("/proc/13608/maps", O_RDONLY) = 3
fstat64(3, {st_mode=S_IFREG|0444, st_size=0, ...}) = 0
mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x55559000
read(3, "00349000-00363000 r-xp 00000000 "..., 4096) = 1046
write(1, "ptr1-ffd1f49a\n", 14) = 14
write(1, "ptr2-ffd1f4a8\n", 14) = 14
write(1, "Buffer read - 00349000-00363000 "..., 102) = 102
write(1, "\n", 1) = 1
write(1, "ptr1-ffd1f49a\n", 14) = 14
write(1, "ptr2-ffd1f4aa\n", 14) = 14
write(1, "Buffer read - 00367000-004a6000 "..., 104) = 104
write(1, "\n", 1) = 1
write(1, "ptr1-ffd1f49a\n", 14) = 14
write(1, "ptr2-ffd1f4bd\n", 14) = 14
write(1, "Buffer read - 08048000-08049000 "..., 123) = 123
write(1, "\n", 1) = 1
write(1, "ptr1-ffd1f49a\n", 14) = 14
write(1, "ptr2-ffd1f4a1\n", 14) = 14
write(1, "Buffer read - ffad8000-ffaf1000 "..., 95) = 95
write(1, "\n", 1) = 1
write(1, "ptr1-ffd1f479\n", 14) = 14
write(1, "ptr2-ffd1f479\n", 14) = 14
write(1, "Buffer read - ffffe000-fffff000 "..., 55) = 55
write(1, "\n", 1) = 1
read(3, "", 4096) = 0
close(3) = 0
munmap(0x55559000, 4096) = 0
write(1, "Starting Address - 00349000\n", 28) = 28
write(1, "Ending Address - 00363000\n", 26) = 26
write(1, "Permissions - r-xp\n", 19) = 19
write(1, "Offset - 00000000\n", 18) = 18
write(1, "PathName - </lib/ld-2.5.so>\n", 28) = 28
write(1, "\n", 1) = 1
write(1, "\n", 1) = 1
write(1, "Starting Address - 00367000\n", 28) = 28
write(1, "Ending Address - 004a6000\n", 26) = 26
write(1, "Permissions - r-xp\n", 19) = 19
write(1, "Offset - 00000000\n", 18) = 18
write(1, "PathName - </lib/libc-2.5.so>\n", 30) = 30
write(1, "\n", 1) = 1
write(1, "\n", 1) = 1
write(1, "Starting Address - 08048000\n", 28) = 28
write(1, "Ending Address - 08049000\n", 26) = 26
write(1, "Permissions - r-xp\n", 19) = 19
write(1, "Offset - 00000000\n", 18) = 18
write(1, "PathName - </fs_user/samirba/myP"..., 49) = 49
write(1, "\n", 1) = 1
write(1, "\n", 1) = 1
write(1, "Starting Address - ffad8000\n", 28) = 28
write(1, "Ending Address - ffaf1000\n", 26) = 26
write(1, "Permissions - rw-p\n", 19) = 19
write(1, "Offset - 7ffffffe6000\n", 22) = 22
write(1, "PathName - <[stack]>\n", 21) = 21
write(1, "\n", 1) = 1
write(1, "\n", 1) = 1
write(1, "Starting Address - ffffe000\n", 28) = 28
write(1, "Ending Address - fffff000\n", 26) = 26
write(1, "Permissions - r-xp\n", 19) = 19
write(1, "Offset - ffffe000\n", 18) = 18
write(1, "PathName - <EMPTY>\n", 19) = 19
write(1, "\n", 1) = 1
write(1, "\n", 1) = 1
exit_group(0) = ?
There is no one to one relationship between a malloc call and a system call.
Typically, a malloc library will get big blocks from the OS
using e.g. brk system call or mmap system call.
Then these big block(s) will be cut in smaller blocks to serve
successive malloc calls. A free will usually not cause a system call
(e.g. munmap) to be called.
So, you cannot really track malloc and free at system call level.
Valgrind can track the memory leaks because it intercepts (and replaces)
malloc, free, ...
The Valgrind replacements functions are maintaining a list of allocated blocks.
Real leaks (i.e. memory which cannot be reached anymore, i.e. all pointers to it
have been lost/erased) are found by Valgrind using a scan of all the active
memory.
AFAIK, the memory blocks allocated by OS are identified by the starting address. So look for free() that is called with the same argument, which was returned by malloc() previously. As strace logs more low-level mmap and brk calls, use ltrace to log high-level library calls, keeping eye at the return values and arguments.