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// Только для amd64. Компилировать как gcc -ffreestanding -nodefaultlibs -nostartfiles -o test-link test-link.c
#if __STDC_HOSTED__ == 1
#error "Я же сказал: компилировать с -ffreestanding -nodefaultlibs -nostartfiles !!!1"
#endif

#define PATHBUF_SIZE 8192

#include <sys/types.h>
#include <sys/stat.h>

extern long int syscall (long int __sysno, ...);

const char* weird_link = "/srv/home/home";

const char* msg_stat_failed =	"stat failed, code ";
const char* msg_st_mode = 	"st_mode:  ";
const char* msg_st_uid = 	"st_uid:   ";
const char* msg_st_gid =	"st_gid:   ";
const char* msg_st_rdev =	"st_rdev:  ";
const char* msg_st_size =	"st_size:  ";
const char* msg_readlink =	"readlink: ";
const char* msg_readlink_failed = "readlink failed, code ";

long syscall_write(unsigned int fd, const void* buf, size_t count) {
	asm("mov $1, %rax");
	asm("syscall");
}

long syscall_stat(const char* path, struct stat* statbuf) {
	asm("mov $4, %rax");
	asm("syscall");
}

long syscall_readlink(const char* path, char* buf, int bufsz) {
	asm("mov $89, %rax");
	asm("syscall");
}

size_t strlen(const char* s) {
	size_t result = 0;
	while(*s++ != '\0') {
		++result;
	}
	return result;
}

void writeout(const void* buf, size_t count) {
	syscall_write(1, buf, count);
}

void kolkhoz_writell(long long n) {
	if(n < 0) {
		writeout("-", 1);
		kolkhoz_writell(-n);
	} else {
		if(n > 9) {
			kolkhoz_writell(n / 10);
			n %= 10;
		}
		char c = (char) n + '0';
		writeout(&c, 1);
	}
}

void writeline(const void* header, long long value) {
	writeout(header, strlen(header));
	kolkhoz_writell(value);
	writeout("\n", 1);
}

void _start(void) {
	struct stat statbuf;
	char pathbuf[PATHBUF_SIZE];
	long result = syscall_stat(weird_link, &statbuf);
	if(result) {
		writeline(msg_stat_failed, result);
		goto exit;
	}
	writeline(msg_st_mode, statbuf.st_mode);
	writeline(msg_st_uid, statbuf.st_uid);
	writeline(msg_st_gid, statbuf.st_gid);
	writeline(msg_st_rdev, statbuf.st_rdev);
	writeline(msg_st_size, statbuf.st_size);
	result = syscall_readlink(weird_link, pathbuf, PATHBUF_SIZE);
	if(result <= 0) {
		writeline(msg_readlink_failed, result);
		goto exit;
	} else {
		writeout(msg_readlink, strlen(msg_readlink));
		writeout(pathbuf, (size_t) result);
		writeout("\n", 1);
	}
exit:
	asm("mov $0, %rdi\nmov $60, %rax\nsyscall");
}

/nix/store/ajrrkivdfvp8dp4vdg5hp1h5hblmanc9-binutils-2.31.1/bin/ld: /run/user/1000/ccEIhAmP.o: in function `kolkhoz_writell.localalias.1':
check.c:(.text+0x11f): undefined reference to `__stack_chk_fail'
/nix/store/ajrrkivdfvp8dp4vdg5hp1h5hblmanc9-binutils-2.31.1/bin/ld: /run/user/1000/ccEIhAmP.o: in function `_start':
check.c:(.text+0x2c5): undefined reference to `__stack_chk_fail'
collect2: error: ld returned 1 exit status

$ proot -b /tmp:/srv/home/home ./test-link                               ~/tmp +proot +gcc
st_mode:  17407
st_uid:   0
st_gid:   0
st_rdev:  0
st_size:  28672
readlink failed, code -22

/home                ->  /srv/home/home/
/srv/home/home       ->  /srv/.links/*******
/srv/.links/*******  ->  ../disk**/*******

st_mode:  16872
st_uid:   *******
st_gid:   1111
st_rdev:  0
st_size:  61
readlink: /srv/.links/*******

$ mount 
mount: failed to read mtab: No such file or directory
$ cat /proc/self/mountinfo
cat: /proc/self/mountinfo: No such file or directory
$ lsns 
$

$ find -L /etc/systemd/ -type f -exec sh -c 'echo "\n============\n{}\n============"; cat "{}"' \;

============
/etc/systemd/network/50-virtio-kernel-names.link
============
[Match]
Driver=virtio_net

[Link]
NamePolicy=onboard kernel

============
/etc/systemd/system/syslog.service
============
[Unit]
Description=System Logging Service
Requires=syslog.socket
Documentation=man:rsyslogd(8)
Documentation=http://www.rsyslog.com/doc/

[Service]
Type=notify
ExecStart=/usr/sbin/rsyslogd -n
StandardOutput=null
Restart=on-failure

[Install]
WantedBy=multi-user.target
Alias=syslog.service

============
/etc/systemd/system/getty.target.wants/getty@tty1.service
============

[Unit]
Description=Getty on %I
Documentation=man:agetty(8) man:systemd-getty-generator(8)
Documentation=http://0pointer.de/blog/projects/serial-console.html
After=systemd-user-sessions.service plymouth-quit-wait.service
After=rc-local.service

Before=getty.target
IgnoreOnIsolate=yes

Conflicts=rescue.service
Before=rescue.service

ConditionPathExists=/dev/tty0

[Service]
ExecStart=-/sbin/agetty --noclear %I $TERM
Type=idle
Restart=always
RestartSec=0
UtmpIdentifier=%I
TTYPath=/dev/%I
TTYReset=yes
TTYVHangup=yes
TTYVTDisallocate=yes
KillMode=process
IgnoreSIGPIPE=no
SendSIGHUP=yes

Environment=LANG= LANGUAGE= LC_CTYPE= LC_NUMERIC= LC_TIME= LC_COLLATE= LC_MONETARY= LC_MESSAGES= LC_PAPER= LC_NAME= LC_ADDRESS= LC_TELEPHONE= LC_MEASUREMENT= LC_IDENTIFICATION=

[Install]
WantedBy=getty.target
DefaultInstance=tty1

============
/etc/systemd/system/multi-user.target.wants/cron.service
============
[Unit]
Description=Regular background program processing daemon
Documentation=man:cron(8)

[Service]
EnvironmentFile=-/etc/default/cron
ExecStart=/usr/sbin/cron -f $EXTRA_OPTS
IgnoreSIGPIPE=false
KillMode=process

[Install]
WantedBy=multi-user.target

============
/etc/systemd/system/multi-user.target.wants/dns-clean.service
============
[Unit]
Description=Clean up any mess left by 0dns-up

DefaultDependencies=false
Before=network-manager.service systemd-networkd.service networking.service resolvconf.service
After=local-fs.target
Requires=local-fs.target

ConditionPathExists=/etc/ppp/ip-down.d/0dns-down

[Service]
Type=oneshot
ExecStartPre=/bin/mkdir -p /var/run/pppconfig
ExecStart=/etc/ppp/ip-down.d/0dns-down "0dns-clean"

[Install]
WantedBy=multi-user.target

============
/etc/systemd/system/multi-user.target.wants/networking.service
============
[Unit]
Description=Raise network interfaces
Documentation=man:interfaces(5)
DefaultDependencies=no
Wants=network.target
After=local-fs.target network-pre.target apparmor.service systemd-sysctl.service systemd-modules-load.service
Before=network.target shutdown.target network-online.target
Conflicts=shutdown.target

[Install]
WantedBy=multi-user.target
WantedBy=network-online.target

[Service]
Type=oneshot
EnvironmentFile=-/etc/default/networking
ExecStartPre=-/bin/sh -c '[ "$CONFIGURE_INTERFACES" != "no" ] && [ -n "$(ifquery --read-environment --list --exclude=lo)" ] && udevadm settle'
ExecStart=/sbin/ifup -a --read-environment
ExecStop=/sbin/ifdown -a --read-environment --exclude=lo
RemainAfterExit=true
TimeoutStartSec=5min

============
/etc/systemd/system/multi-user.target.wants/pppd-dns.service
============
[Unit]
Description=Restore /etc/resolv.conf if the system crashed before the ppp link was shut down

[Service]
Type=oneshot
ExecStart=/etc/ppp/ip-down.d/0000usepeerdns

[Install]
WantedBy=multi-user.target


============
/etc/systemd/system/multi-user.target.wants/remote-fs.target
============

[Unit]
Description=Remote File Systems
Documentation=man:systemd.special(7)
After=remote-fs-pre.target
DefaultDependencies=no
Conflicts=shutdown.target

[Install]
WantedBy=multi-user.target

============
/etc/systemd/system/multi-user.target.wants/rsync.service
============
[Unit]
Description=fast remote file copy program daemon
ConditionPathExists=/etc/rsyncd.conf

[Service]
ExecStart=/usr/bin/rsync --daemon --no-detach

[Install]
WantedBy=multi-user.target

============
/etc/systemd/system/multi-user.target.wants/rsyslog.service
============
[Unit]
Description=System Logging Service
Requires=syslog.socket
Documentation=man:rsyslogd(8)
Documentation=http://www.rsyslog.com/doc/

[Service]
Type=notify
ExecStart=/usr/sbin/rsyslogd -n
StandardOutput=null
Restart=on-failure

[Install]
WantedBy=multi-user.target
Alias=syslog.service

============
/etc/systemd/system/network-online.target.wants/networking.service
============
[Unit]
Description=Raise network interfaces
Documentation=man:interfaces(5)
DefaultDependencies=no
Wants=network.target
After=local-fs.target network-pre.target apparmor.service systemd-sysctl.service systemd-modules-load.service
Before=network.target shutdown.target network-online.target
Conflicts=shutdown.target

[Install]
WantedBy=multi-user.target
WantedBy=network-online.target

[Service]
Type=oneshot
EnvironmentFile=-/etc/default/networking
ExecStartPre=-/bin/sh -c '[ "$CONFIGURE_INTERFACES" != "no" ] && [ -n "$(ifquery --read-environment --list --exclude=lo)" ] && udevadm settle'
ExecStart=/sbin/ifup -a --read-environment
ExecStop=/sbin/ifdown -a --read-environment --exclude=lo
RemainAfterExit=true
TimeoutStartSec=5min

============
/etc/systemd/system/sysinit.target.wants/systemd-timesyncd.service
============

[Unit]
Description=Network Time Synchronization
Documentation=man:systemd-timesyncd.service(8)
ConditionCapability=CAP_SYS_TIME
ConditionVirtualization=!container
DefaultDependencies=no
RequiresMountsFor=/var/lib/systemd/clock
After=systemd-remount-fs.service systemd-tmpfiles-setup.service systemd-sysusers.service
Before=time-sync.target sysinit.target shutdown.target
Conflicts=shutdown.target
Wants=time-sync.target

[Service]
Type=notify
Restart=always
RestartSec=0
ExecStart=/lib/systemd/systemd-timesyncd
WatchdogSec=3min
CapabilityBoundingSet=CAP_SYS_TIME CAP_SETUID CAP_SETGID CAP_SETPCAP CAP_CHOWN CAP_DAC_OVERRIDE CAP_FOWNER
PrivateTmp=yes
PrivateDevices=yes
ProtectSystem=full
ProtectHome=yes
ProtectControlGroups=yes
ProtectKernelTunables=yes
MemoryDenyWriteExecute=yes
RestrictRealtime=yes
RestrictAddressFamilies=AF_UNIX AF_INET AF_INET6
SystemCallFilter=~@cpu-emulation @debug @keyring @module @mount @obsolete @raw-io

[Install]
WantedBy=sysinit.target

============
/etc/systemd/system/timers.target.wants/apt-daily-upgrade.timer
============
[Unit]
Description=Daily apt upgrade and clean activities
After=apt-daily.timer

[Timer]
OnCalendar=*-*-* 6:00
RandomizedDelaySec=60m
Persistent=true

[Install]
WantedBy=timers.target

============
/etc/systemd/system/timers.target.wants/apt-daily.timer
============
[Unit]
Description=Daily apt download activities

[Timer]
OnCalendar=*-*-* 6,18:00
RandomizedDelaySec=12h
Persistent=true

[Install]
WantedBy=timers.target

============
/etc/systemd/system/timers.target.wants/phpsessionclean.timer
============
[Unit]
Description=Clean PHP session files every 30 mins

[Timer]
OnCalendar=*-*-* *:09,39:00
Persistent=true

[Install]
WantedBy=timers.target

============
/etc/systemd/journald.conf
============

[Journal]

============
/etc/systemd/logind.conf
============

[Login]

============
/etc/systemd/resolved.conf
============

[Resolve]

============
/etc/systemd/system.conf
============

[Manager]

============
/etc/systemd/timesyncd.conf
============

[Time]

============
/etc/systemd/user.conf
============

[Manager]